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3Genetics, Conception, and Prenatal Development

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Learning Objectives

After completing this chapter, you should be able to:

• Understand the genetic foundations of development and explain the purpose of genetic counseling.

• Identify common genetic abnormalities.

• Explain the process of conception and in utero human development.

• Summarize factors that contribute to variability in prenatal outcomes, including maternal nutrition and threats to the prenatal environment.

• Explain when the three major types of prenatal tests are used and how they differ.

• Outline the risk factors associated with infertility and summarize choices in assisted reproductive technology.

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Prologue

Chapter Outline

Prologue

3.1 Genetic Foundations Dominant and Recessive Alleles Transmission of Genes Genetics and the Environment

3.2 Genetic Variations Sex-Linked Genetic Variations Intersex and Other Sex Variations Down Syndrome Genetic Testing and Counseling

3.3 Conception and Prenatal Development Conception and Germinal Period Embryonic Period Fetal Period

3.4 Environmental Influences in Prenatal Development Nutrition Exercise Mental Health Age Prenatal Care and Socioeconomic Status Threats to Prenatal Development Critical and Sensitive Periods of Development

3.5 Prenatal Tests Ultrasound Chorionic Villus Sampling Amniocentesis Blood Tests

3.6 Infertility and Reproductive Choice Secondary Infertility Choices in Reproduction

Summary & Resources

Prologue At the beginning of the last century, making a baby seemed like a relatively carefree undertak- ing. Two people got married, had intercourse, and, if everything went as planned, had a baby. Sometimes the order of operations was different, and shotgun weddings were involved, but the outcome was about the same. Less was known about good nutrition, and a healthy vari- ety of uncontaminated food was not always widely available. Parenting duties were usually the domain of mothers or female extended family members. Of the vaccinations that were

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Section 3.1 Genetic Foundations

available, few were administered. “Childproofing” a home was not yet part of popular vocabu- lary. Infants died of mysterious contaminants and not so mysterious viruses at an alarming rate. And delivery complications that resulted in the deaths of mothers, infants, or both were not uncommon.

In the new millennium, infants enter the developed world in a dramatically different way than they did 100 years ago. Among certain demographics, single motherhood is the norm; most women in the United States give birth in safe hospitals that reduce complications rather than increase the risk of death. And because of advances in genetic engineering and reproduc- tive medicine, health care professionals can diagnose and even treat a number of conditions before an infant is born. We will take a look at some of these processes, including genetic and technological issues of conception and prenatal (before birth) development.

3.1 Genetic Foundations It is sometimes amazing to regard the diversity of humans on the planet. Though there are bil- lions of people, each can be distinguished from others by individual characteristics. Many of the physical differences are inherited from parents through specific genes. Preprogrammed, inherited characteristics, such as height, eye color, shape of the earlobe, and hairline, are iden- tifiable in one’s genotype, the genetic code for an organism. Except in identical twins, differ- ent genotypes explain why we all look so different. A person’s genotype provides the instruc- tions for maturational processes.

Genotypes interact with the environment to produce other, more varied characteristics. For example, inherited genotypes for intelligence, humor, and motor skills affect an individual’s school performance, personality, and athletic achievement. Parents pass on several genes that contribute to height (the genotype), but there is only one final stature. The observable expres- sion of the “height” genotype, including how it was modified through the environment, refers to a person’s phenotype—the expression of athletic skills, the ability to make friends, and the degree to which hair color changes as a result of stress all represent phenotypes. Psycholo- gists most often study phenotype characteristics and behaviors, which they often refer to as traits.

Dominant and Recessive Alleles For each gene, humans have a set of two alleles, one of which is inherited from each parent. How the two alleles interact contributes to how the gene is expressed. One allele sometimes determines outcome, regardless of its counterpart. Other times, the alleles need to be identi- cal for a given outcome to occur. When the two alleles are identical, we say that we are homo- zygous for that gene (or trait); when they are different, they are heterozygous.

Alleles can be either dominant or recessive. The trait of a recessive allele will be expressed only if both inherited markers for that trait are recessive (homozygous recessive). For exam- ple, cystic fibrosis is caused by one defective gene. The disease inhibits breathing, causes digestive problems, serious lung infections, poor growth, and a host of other symptoms. The phenotype for cystic fibrosis will occur only if both parents transmit the cystic fibrosis allele (the recessive trait), resulting in a homozygous recessive genotype. As shown in Figure 3.1,

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c = Recessive allele for cystic �brosis

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Section 3.1 Genetic Foundations

any other allele will dominate over the cystic fibrosis allele, so children who are heterozygous for cystic fibrosis will never have the disease. (A homozygous dominant gene will neither cause the disease nor be able to transmit the gene to the next generation.) In this example, the odds of a child getting the disease are one in four. For this reason, the issue of dominant and recessive alleles is especially important in studying development. A harmful recessive trait can be inherited for many generations (hundreds or even thousands) without any effect until it is joined with another recessive carrier.

Figure 3.1: Dominant and recessive alleles

In order for children to have cystic fibrosis, they must inherit the recessive allele from both parents.

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c = Recessive allele for cystic �brosis

C = “Normal” allele (no cystic �brosis)

Transmission of Genes A human’s entire genetic code is determined by the unique combination of a single ovum (egg) from the mother and a single sperm cell from the father. These cells are the reproduc- tive cells, or gametes. Within each cell are chromosomes, which store the genetic informa- tion. The ovum and the sperm carry the genetic information that will direct development. These sex cells are the only cells in the body that contain 23 chromosomes. (Interestingly, ova

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Section 3.1 Genetic Foundations

are the largest cells in the human body—typically visible to the unaided eye—and sperm are the smallest.)

Gametes contain a central structure called the nucleus, which holds the chromosomes. When the two sets of 23 chromosomes unite, they form 46 chromosomes (23 pairs). Half of each pair is from the father and half is from the mother. Each set of chromosomes contains DNA (deoxyribonucleic acid), a molecule that contains instructions on replication that will even- tually turn one cell into trillions—each of which will contain the identical genetic code of the original. The DNA in each chromosome has a twisted, double helix shape, as shown in Figure 3.2. Along the short segments of DNA are genes, which specifically carry hereditary informa- tion and are therefore located at specific sites on the chromosome.

Figure 3.2: Structure of a chromosome

The cell body (top right) contains the nucleus. The nucleus contains 23 pairs of chromosomes, threadlike structures, which are composed of DNA. Genes are segments of DNA that contain hereditary information.

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Section 3.1 Genetic Foundations

One way to look at the relationship between the terms is by this analogy: Chromosomes are like books; DNA represents the words, and genes are the letters. Each chromosome carries hundreds or thousands of genes. The complete set of instructions for making a human would be like having an entire library.

This metaphorical library became a reality in 2003 when the Human Genome Project and the Celera Corporation completed a map of the human genetic code (Gregory et al., 2006). Though it was initially predicted that there were more than 100,000 human genes, it was found that there are only between 20,000 and 25,000 human genes that are involved in cod- ing. Another of the many advances of the Human Genome Project was the discovery that so many genes do not function independently, and therefore many traits are due to polygenetic inheritance. Additionally, single genes sometimes have an effect on multiple traits. Research- ers found that genes usually interact with other genes and with the environment, turning on and off depending on biological and environmental circumstances. For instance, ultraviolet radiation alters the chemistry of the genotype for skin color and modifies the effect of aging on vision; type 2 diabetes may or may not occur because of environmental mechanisms that interact with the genome. This two-way interaction is the process of epigenesis, as described in Chapter 1.

Genetics and the Environment The contemporary discussion regarding the interaction of genes and the environment dates to the late 1800s, when Francis Galton, Charles Darwin’s cousin, first wrote that, “Nature is all that a man brings with himself into the world; nurture is every influence from without that affects him after his birth” (Galton, 1895). Today, virtually all theories of development include an interactionist approach, introduced in Chapter 1, that recognizes the influences of both nature and nurture, and research professionals agree that both nature and nurture have important functions in nearly every area of development. Therefore, debates center on the rel- ative importance of an organism’s innate biological features versus its personal experiences.

Sandra Scarr and her colleagues offer a linear model of this interaction by describing three different ways that hereditary predisposition affects the environment (Scarr & McCartney, 1983). Children become linked to environments because they are born with particular traits. Stated another way, some children are more sensitive to a particular environment because of a particular genetic predisposition (Plomin, 2013). Scarr and McCartney describe three patterns:

• Passive genotype-environment effects occur when children have no control over the relationship between their genes and the environment. These effects occur more often when children are younger, but they occur at older ages as well. For instance, parents who are brilliant athletes may promote good physical education; parents who play instruments may provide opportunities to excel musically; academic parents are more inclined to promote reading and studying than are nonacademic parents. In these ways, children are likely to excel because of both genetic and envi- ronmental factors.

• Evocative genotype-environment effects occur when children’s genetic predis- positions evoke responses from others. Talkative, articulate children generally elicit more positive social responses from adults than do quiet children; a child playing soccer at a friend’s house may draw the attention of parents and other adults who

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Section 3.2 Genetic Variations

3.2 Genetic Variations Single genes sometimes result in predictable phenotypes, such as that for Huntington’s dis- ease. Often though, there is polygenetic inheritance (many genes), as in the earlier example with height. Because several genes are involved in the expression of height, the phenotype cannot be predicted with any certainty. Each dominant allele for height will add to the final genotype. (And sometimes there may be no dominant alleles at all.) Similarly, geneticists have discovered specific genes in the transmission of type I diabetes, but these genes do not always result in the same outcome. That is, different combinations of genes may or may not produce diabetes. Unlike Huntington’s disease, any two individuals with type I diabetes do not neces- sarily have the same genetic footprint.

Sometimes genes reproduce out of sequence or otherwise change. These gene mutations are sometimes beneficial by aiding survival and at other times are harmful. Mutations are actually the cornerstone of evolutionary adaptation. The first curiously tall giraffes were the result of mutated genes. But as those giraffes remained better fed (by reaching more food), they were more likely to reproduce and pass on their mutated genes. They became the most fit to survive. For humans, it is well known that in areas of Sub-Saharan Africa, where

see athletic potential. Naturally aggressive children are more likely to evoke harsher punishment than children who are more passive. Based on their innate character- istics, children capture the attention of adults when they do things like write, read, play music or sports, or show artistic ability. The responses that they evoke from others reinforce hereditary potential.

• Active (niche-picking) genotype-environment effects are more common in older children, who can more easily extend their experiences outside of their families. They can actively pursue the stimulation of an available niche depending on their particular genotype, including those related to specific skills (such as music, reading, sports, or art) or personality (such as introversion or extroversion).

Therefore, in this unidirectional view, a person’s genotype directs experience.

By contrast, the epigenetic view of development, introduced in Chapter 1, holds that the inter- action of heredity and the environment is continuous and bidirectional. Epigenesis says that there is collaboration between genes and the environment (heredity � environment), rather than the unidirectional relationship suggested by Scarr and McCartney (heredity � environ- ment). The environment influences how genes are expressed and gene expression influences how we react to the environment. For instance, overeating and obesity influence (and mod- ify) the expression of genes that affect the onset of some diseases, such as diabetes. Genes alone do not cause either obesity or its associated diseases, but certain behaviors may turn disease genes either on or off (Gottlieb, 2007).

Section Review Explain the relationship between chromosomes and genes and how traits are inherited.

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Section 3.2 Genetic Variations

malaria is common, a relatively high number of individuals carry the allele for sickle cell disease, perhaps over 50% (Elguero et al., 2015). In sickle cell disease, the body makes ineffi- cient sickle-shaped red blood cells that carry oxygen, instead of round ones. Therefore, people with sickle cell dis- ease commonly have problems trans- porting oxygen to the body, a condition called anemia (“sickle cell anemia”). However, those who carry one reces- sive allele for sickle cell disease do not get nearly as ill from malaria as those who do not carry the sickle cell allele. This advantage results from incom- plete dominance of the sickle cell allele over the non-sickle cell allele (a person would be heterozygous for sickle cell disease). Apparently, having the allele became an evolutionary adaptation that aids survival in areas where malaria is common. As a result, children who are heterozygous for sickle cell disease in that part of the world have been more likely than others to reach adulthood and reproduce. In this case, the mutated sickle cell gene contributed to greater fitness, or reproductive success (Gong, Parikh, Rosen- thal, & Greenhouse, 2013).

The sickle cell mutation is unusual in that it also has a harmful side, as noted: Someone who is homozygous recessive for sickle cell will have the disease. Like cystic fibrosis, the child of two parents who are both heterozygous for sickle cell disease has a one in four chance of becom- ing homozygous and inheriting the disease.

Another example of this kind of chance circumstance occurs with Tay-Sachs disease, a neu- rological disorder that typically appears at around 6 months of age. A defect in one gene causes an enzyme inefficiency that leads to the premature death of nerve cells in the brain. The deterioration of mental and motor abilities follows, leading to such conditions as deaf- ness, blindness, and dementia. Tay-Sachs does not have a cure, and most children with the disease die before the age of 4 years (National Institutes of Health, 2015). It has a particularly high prevalence among Jews of Eastern European descent, so people may carry the recessive trait for many generations until they meet another person with the same trait, perhaps with the same ethnic ancestry.

Sex-Linked Genetic Variations As noted earlier, half of the 46 inherited chromosomes are from the father and half are from the mother. Two of them (one pair) are sex chromosomes. A female has two X sex chromo- somes, a pattern designated XX; a male has one X and one Y (XY). A mother (XX) always trans- mits an X chromosome because she has only two and they are both X. If the father transmits an X chromosome, the baby will be a girl (XX); if he transmits a Y, it will be a boy (X from the mother + Y from the father = XY = boy).

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Sickle cell disease is a recessive genetic blood disorder characterized by red blood cells that assume an abnormal, rigid, sickle shape.

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Section 3.2 Genetic Variations

This information is important because X chromosomes are much longer than Y chromosomes and therefore carry more genes. One effect of this difference is that there are some X-based genes that have no equivalent Y genes. These X-linked genes will be expressed in males even if they are recessive, because there is no linked pair to counteract its effects. The expression of the X-linked gene occurs much less often in females because the other X chromosome may be dominant. Therefore, when an abnormal gene is carried only on one sex chromosome, it affects males and females differently. For instance, color-blindness is an X-linked variation. A boy will be born color-blind if he inherits the gene for color-blindness from his mother. A girl will be color-blind only if she inherits markers from both her mother and her father.

A much more serious X-linked variation occurs in Fragile X syndrome, which is the lead- ing cause of inherited intellectual disabilities. In Fragile X, a single gene affects the develop- ment of the central nervous system, causing mild to moderate intellectual impairment. Often, but not always, it is associated with distinctive physical features including a long face, large ears, and short stature. Because it is X-linked, it affects approximately twice as many males as females (Schwarte, 2008; Webb & Bundey, 1991).

Intersex and Other Sex Variations Sometimes there are inconsistencies between chromosomal sex development (genotype) and anatomical development (phenotype). These conditions were previously referred to as her- maphroditism, but medical professionals have been using the more descriptive term disorders of sexual development to broadly include a number of conditions. This term also is rooted in controversy as some observers suggest that a medical disorder of sexual development should not be enough to define a person from a psychosocial perspective (Davis, 2013; Holmes, 2011). Psychologists often use the broader term intersex to describe a chromosomal woman who has the external genitalia of a man, a chromosomal man who has the external genitalia of a woman, or an individual who is born with both ovarian and testicular tissue. These cases are relatively rare, having a combined incidence of about 1 in 5,500 births (Allen, 2009).

There is also some controversy over other classifications, specifically whether or not sexual development should be categorized along a continuum of many different sexes, or as a dichot- omy using male and female as singular, strict distinctions (see, especially, Fausto-Sterling, 1993, and Sax, 2002). For instance, sometimes sex chromosomes are not only XX or XY; addi- tional chromosomes (or the absence of one) changes outward appearance. To reconcile part of the controversy, most clinicians and researchers do not consider individuals to be intersex when genital phenotype is clear, as in the variations of sexual development that follow.

Klinefelter’s syndrome is a chromosomal abnormal- ity that occurs in about 1 in 1,000 males. People with this syndrome are born with one extra sex chromosome (XXY) and sometimes even more. As adults, individuals with Klinefelter’s syndrome produce lower than normal amounts of testosterone and have more female physi- cal features, such as enlarged breasts, curved hips, and more rounded features. As a result, hormone treat- ment is often prescribed to increase the development of male secondary sex characteristics (distinguish- ing characteristics of males and females that typically

Critical Thinking

Many psychologists advocate letting chil- dren decide for themselves whether or not to have hormone treatments for chro- mosomal abnormalities like Klinefelter’s syndrome. What are some advantages and possible drawbacks to allowing children to decide for themselves?

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Section 3.2 Genetic Variations

appear during puberty, such as facial hair growth for boys). Fertility is typically reduced as well (Bock, 1993).

Turner syndrome affects about 1 in 2,500 girls and is marked by a missing X sex chromo- some (instead of XX, there is only one X). Individuals with Turner syndrome are usually infer- tile and do not undergo typical pubertal development unless they receive hormone treat- ment. On average, girls with Turner syndrome typically have normal intelligence but have an increased prevalence of learning disabilities, especially on nonverbal tasks like math (Dav- enport, Ross, & Backeljauw, 2013). There are other, less common, chromosomal abnormali- ties as well, like Triple X and XYY. These conditions are associated with an increased risk of physical delays and learning disabilities, but the majority of individuals are unaware of their abnormal genetic makeup unless there is a reason to undergo genetic testing.

Down Syndrome Chromosomal abnormalities occur as a result of the environment interacting with genetics in a way that is not fully understood. Perhaps the best-known chromosomal abnormality is Down syndrome, a developmental disorder characterized by moderate to severe deficits in physical and cognitive functioning. Typical physical features include short stature, flat facial features, and almond-shaped eyes. Individuals are also at higher risk for vision and hearing problems, heart defects, and even Alzheimer’s disease (Grieco, Pulsifer, Seligsohn, Skotko, & Schwartz, 2015).

Instead of two chromosomes on the 21st pair, people with Down syndrome have three; hence, this disorder is also called Trisomy 21. The extra chromosome usually originates in the female ova, but in about 5% of cases it originates in sperm (Antonarakis & the Down Syndrome Col- laborative Group, 1991). Little is known about the cause of Down syndrome. The only known risk factor is increasing age of the mother, as shown in Figure 3.3 (Hsu, 1998). Among women younger than 25 years, the risk of Down syndrome is 1/1,600; the risk increases to 1/250 for women between the ages of 35 and 39, 1/25 for women over 45 (Canfield et al., 2006), and perhaps even as high as 1 in 2 births for women over the age of 55 (Morris, Wald, Mutton, & Alberman, 2003).

Changes in prevalence of Down syndrome continue to be associated most closely with mater- nal age rather than any other cause (Egan et al., 2011; Natoli, Ackerman, McDermott, & Edwards, 2012; Rousseau et al., 2010). However, researchers have also become increasingly interested in the effect of advanced paternal age on developmental outcomes. A landmark study by Fisch et al. (2003) found the effect of maternal age on Down syndrome becomes stronger when paired with advanced age of the father (see Figure 3.4). Though little paternal effect is found if mothers are aged 35 and younger, it appears to be quite strong when mothers are older than 40. That is, when mothers are younger, the genetic contribution of fathers does not appear to influence the prevalence of Down syndrome. However, if mothers are older than 40, there are fewer cases of Down syndrome if the fathers are younger rather than older. The paternal contribution to Down syndrome among the older group was found to be as high as 50%.

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Section 3.2 Genetic Variations

As a result of gene mapping and other technological advances, strong evidence has been accumulating that point to associations between paternal age and other disease risks as well. These include autism, mental health problems, attention-deficit/hyperactivity disorder, and low academic performance (D’Onofrio et al., 2014; Idring et al., 2014). Groundbreaking research by Kong et al. (2012) concluded that gene mutations transmitted by fathers in gen- eral are “dominated by the age of the father at conception of the child” (p. 471). Every year of increasing paternal age was associated with two gene mutations passed on to offspring. With birth rates among older fathers continuing to accelerate, this is an increasing concern (Fisch, 2013; Holohan et al., 2015; Momand, Xu, & Walter, 2012; Ramasamy, Chiba, Butler, & Lamb, 2015).

Figure 3.3: Risk of Down syndrome, by maternal age

The risk of infants being born with Down syndrome (Trisomy 21) increases significantly with the age of the mother.

Source: David S. Newberger, M.D., “Down Syndrome: Prenatal Risk Assessment and Diagnosis,” American Family Physician, 62(4): 825–832, Figure 1. Reprinted by permission of the American Academy of Family Physicians.

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Section 3.2 Genetic Variations

Figure 3.4: Rate of Down syndrome birth, by maternal and paternal age

Prevalence of Down syndrome among children of fathers and mothers of various ages. Down syndrome occurs in about 300 out of 100,000 births of children whose mothers and fathers are 24 and younger. Among mothers 40 and older, the ratio increases substantially as a function of the age of the father.

Source: H. Fisch et al., “The Influence of Paternal Age on Down Syndrome,” The Journal of Urology 169(6): 2275–8. Copyright . 2003. Reprinted by permission of Elsevier.

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Genetic Testing and Counseling Because the average age of childbearing women has continued to increase worldwide over the past two generations, screening for genetic abnormalities (see section 3.5) has become an increasingly important health care strategy. A simple blood test can be administered during the pregnancy-planning phase to identify recessive anomalies and other genetic variations. If testing takes place after conception, advance knowledge of fetal abnormalities allows parents to better prepare themselves for a special needs child or to consider pregnancy termination. Genetic counselors help translate the constantly evolving world of genetics into something meaningful for those who can benefit from it, and they work in a wide range of settings. They are found in many types of hospital settings, including pediatric, cancer, and neurological clin- ics. Some work for the government or insurance companies developing policies. Others are in laboratories or biotech companies.

Genetic testing is most often used for screening newborn infants for abnormalities like Tay- Sachs, sickle cell disease, and cystic fibrosis. If medical problems are detected, sometimes

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Section 3.3 Conception and Prenatal Development

3.3 Conception and Prenatal Development As you have seen, the genetic course of development is influenced even before an egg is fertil- ized. The typical full-term human gestational period (time of prenatal growth) lasts 266– 280 days (38–40 weeks) from date of conception, ending at birth. The entire period is usually divided into three periods: germinal, embryonic, and fetal. Unlike scientists and research- ers, however, doctors, parents, and the media will often divide the period into trimesters, or thirds, so it is useful to understand the associated milestones with respect to both approaches (see Figure 3.5).

Next, we look at biological beginnings, starting with conception, and then cover each of the gestational periods.

Conception and Germinal Period Pregnancy begins with conception. One sperm joins with one ovum to begin the task of devel- opment. During intercourse, a man ejaculates, on average, a quarter of a million sperm. The sperm are manufactured in the testes, which also produce the male hormone testosterone. Before leaving the penis through the urethra, sperm are mixed with other fluids to provide lubrication and to increase mobility (see Figure 3.6).

During a typical month, the testes manufacture millions of sperm. A woman will release, on average, one egg every 28 days. The eggs are released from one of two ovaries, the organs in female vertebrates that produce eggs. The fimbria (plural, fimbriae) “sweeps” the egg into the fallopian tube, which is the pathway to the uterus.

interventions can be performed on a fetus. For instance, fetuses can be the recipients of drug injections and blood transfusions.

In addition to gathering data about inherited diseases and pregnancy complications like repeated unsuccessful pregnancies, genetic counselors collect information about mental dis- orders, emotional problems, and physical conditions like heart disease and stroke within the parents’ extended family (Larry Prensky, personal communication, 2015). When appropriate, they advise a course of family planning options that could include the use of reproductive technology or management of a genetic condition. Counseling can occur before conception if it is known that one or both parents are carriers of abnormal traits or mid-pregnancy when a prenatal test has abnormal results. Finally, they are also called upon after births as social workers for children who need special support services.

Section Review Describe some common genetic abnormalities, including their typical phenotypes.

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Section 3.3 Conception and Prenatal Development

Figure 3.5: Prenatal periods of development

The prenatal period is often divided into distinct periods. Though scientists and researchers often refer to the germinal, embryonic, and fetal periods, the entire period may also be divided into thirds called trimesters.

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Section 3.3 Conception and Prenatal Development

While the egg travels partway down the fallopian tube, sperm are finding their way up. Although ova survive only about a day, sperm can live as long as six days, so the window of opportunity for pregnancy can potentially last up to a week. As shown in Figure 3.7, sperm make their way through the vagina, past the cervix, into the uterus, and finally into the fal- lopian tube. Only a few hundred sperm survive to the fallopian tube and only one will be used there for fertilization.

After the egg is fertilized, it is called a zygote. The zygote begins to divide methodically as it makes its way through the fallopian tube to the uterus (the womb). It reaches the uterus in about 7 days, which by this time has thickened with blood to provide nourishment. The ball of cells takes another week or so to implant itself in the uterine wall. This germinal period (also called the period of the zygote) lasts approximately 2 weeks until the ball of cells becomes fully implanted. When this change is complete, it becomes known as an embryo. If implanta- tion does not take place, the thickened uterine wall serves no purpose and is sloughed off, or shed. This last phase of the cycle is commonly referred to as the menstrual period.

Figure 3.6: Male reproductive anatomy

Sperm are manufactured in the testes, which are protected by the scrotum. During ejaculation, the sperm travel up the vas deferens where they mix with fluids from the seminal vesicle, ejaculatory duct, prostate gland, and Cowper’s gland before being ejaculated through the urethra. Mixed together, these fluids are called semen.

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endometriumfimbria fimbria

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Section 3.3 Conception and Prenatal Development

Because identifying an exact date of conception is difficult, research usually defines a typical pregnancy as 40 weeks (for scientific pursuits, the operational definition), beginning from the date of the woman’s last period. Table 3.1 identifies the developmental milestones that occur during the germinal period.

Table 3.1: Germinal period milestones (conception – week 2)

Day Event

1 First trimester begins; fertilization (usually within 24 hours of ovulation).

2 Division of cells by cleavage (cell division without an increase in overall mass); zygote travels from fallopian tube towards uterus; zygote is now 4 cells.

3 The zygote now consists of 8 cells.

4 Ball of 16-32 cells is now called a morula; preparing for cell differentiation, which marks transition to blastocyst phase.

5 The cells are now a hollow mass called a blastocyst, containing about 150 cells; inner and outer cells are differentiated.

6–7 The blastocyst begins attachment to the wall of the uterus.

14 The blastocyst is now fully embedded; transition to gastrulation.

Figure 3.7: Female reproductive anatomy

After the egg is released from the ovary, it is swept into the fallopian tube by the fimbriae. The egg is fertilized in the fallopian tube by a single sperm that has traveled into the vagina and past the uterus. The fertilized egg, called a zygote, begins to divide as it continues to travel through the fallopian tube. After 5–7 days, the hollow mass of cells—now called a blastocyst—begins the process of implantation into the lining of the uterus. It will take another week before implantation is complete.

fallopian tubes

ovary egg

(ovum) cervix

uterus

fertilization

zygotecell duplication

ovary

vagina

sperm

endometriumfimbria fimbria

implantation

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Section 3.3 Conception and Prenatal Development

Embryonic Period The third week begins the embryonic period, which lasts until the end of week 8 (see Table 3.2). All vital organ structures, including the heart, muscles, and digestive tract begin their primitive development, in a process called organogenesis. External features like hands, feet, eyes, and ears also appear, and the embryo can begin to move. Most miscarriages (also called spontaneous abortions) occur during the early part of this period. It has been estimated that about 25% of embryos are miscarried within 4 weeks of conception, often without the woman being aware she was pregnant (Hure et al., 2012; Wang et al., 2003). The high rate of spontaneous abortion during the first month of pregnancy is thought to be nature’s way of protecting the species, for about half of miscarried embryos during this period have chromo- somal abnormalities (Dória et al., 2009).

Growth occurs rapidly, as implantation means a constant supply of blood and nutrients. The placenta develops in order for the embryo to exchange food, waste, blood, and oxygen with its mother’s blood supply. The placenta connects to the mother by way of the umbilical cord at the abdomen (later forming the “belly button”). The nervous system becomes extraordi- narily active in the proliferation of neurons. By the end of the embryonic period and continu- ing through 18 weeks after conception, approximately 200,000 neurons are produced every minute (Lagercrantz & Ringstedt, 2009).

Table 3.2: Embryonic period milestones (week 3 – week 8)

Week Event

3 Gastrulation, the process of cell migration to form three different layers of tissue; the outer ectoderm, the middle mesoderm, and the inner endoderm. Neural plate forms.

4 Primitive neural tube develops; heart begins beating.

5 Structures like ears, nose, mouth and limbs take shape; organogenesis.

7 Brain structures begin to differentiate.

8 Organs (including ovaries and testes) are now present; digits separate; coordinated hand move- ments begin.

Fetal Period The developing organism from about the eighth week post-conception until birth is referred to as the fetus. At the beginning of the ninth week, the embryo can be identified as human (though perhaps misshapen) and is about one inch (2.5 cm) long. Thus begins the fetal period, which lasts from the end of the embryonic period until birth (see Table 3.3). By week nine bones have begun to form, including clear elongation of fingers and toes; the central ner- vous system has organized and muscles show coordination, as evidenced by the fetus turning its head and opening and closing its mouth.

During the middle of the pregnancy, the fetus grows a special kind of delicate hair called lanugo, which covers the body. This hair protects the skin and helps a waxy substance called vernix to adhere. Vernix helps protect the skin of the fetus as it grows in the womb and will later aid in lubricating the passage through the birth canal. Fetuses will voluntarily move into a favorite sleep pattern and may react to loud sounds.

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Section 3.3 Conception and Prenatal Development

When infants are first able to survive outside the womb, it is called the age of viability. As medical technology has improved, the age of viability has decreased, though a plateau has occurred in recent years. Even though countries with similar advanced medical technology have variable rates of infant mortality (the death of an infant that occurs before one year), international practices are fairly consistent: Infants are generally given full resuscitation at 24 weeks gestation. That is, though there are strong concerns about their efficacy, chest com- pressions and epinephrine will be administered to facilitate breathing and blood flow (e.g., Handley, Sun, Wyckoff, & Lee, 2015; Perkins, Cottrell, & Gates, 2014). At 22 weeks or less, only comfort care is provided; babies are kept as pain free as possible, and medical procedures are

Figure 3.8: Severity and type of disability among infants born prior to 26

weeks gestation

Though the age of viability has increased as medical technology has improved, infants born early are still at risk for certain disabilities.

Source: Adapted from Marlow, N., Wolke, D., Bracewell, M. A., & Samara, M. (2005). Neurologic and developmental disability at six years of age after extremely preterm birth. New England Journal of Medicine, 352, 9–19. (Table 3)

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Section 3.3 Conception and Prenatal Development

avoided (Fanaroff et al., 2014). This age range is consistent with the United States as well, although there are substantial regional variations depending on local practices and state laws. In the United States, parental preferences hold significant weight for infants less than 26 weeks (see Figure 3.8) (Arzuaga & Meadow, 2014).

The 26-week marker is identified by the presence of surfactant in the lungs, a substance that keeps the lungs from collapsing and therefore allows exchange of oxygen and carbon dioxide. Without it, breathing assistance along with surfactant therapy is essential. The problem is that infants who require mechanical ventilation and surfactant therapy are also at substantially higher risk of death or lifetime complications, as shown in Figure 3.8 (Dayasiri, Rajasekara, Gamage, Hemachandra, & Edirisinghe, 2014; Neubauer, Voss, & Kattner, 2008). In addition to neuromotor and cognitive disabilities, vision and hearing impairments are also common. Up to half of children born at the edge of viability do not survive, and up to half of those that do survive are at high risk of cognitive, motor, or perceptual disabilities (Glass et al., 2015).

Table 3.3: Fetal period milestones (week 9 – birth)

Week Event

9 Bone tissue develops.

10 Fingers and toes are clearly differentiated.

11 Cerebral hemisphere differentiated from cerebellum and spinal cord.

12 Sex organs begin differentiation into male or female; immature eggs and sperm are forming, though they will not be mature until many years later after the start of puberty.

13–16 Second trimester begins; head is erect; lungs rehearse breathing; organs begin functioning; fetal heartbeat is audible with a stethoscope; fetus uses facial muscles to display different expressions.

16 Sucking and swallowing reflexes emerge; bones visible; eyes have moved forward.

18 Mothers can feel movement; vernix covers skin; fetus 320g (11.3 ounces).

20 Control of movement is evident, including reaction to sounds; lanugo is visible.

21 Average weight is 500g; rapid eye movements (REM) are seen.

23 Age of viability, but high risk of neurodevelopmental deficits; lungs not yet sufficiently developed to prevent fluid accumulation.

26 Third trimester begins; lungs capable of unassisted gas exchange; fetal growth (and hence weight gain for the mother) is most rapid during this phase; cerebral cortex separates into lobes; nearly identical in appearance to full-term fetus.

28 Development of the brain and nervous system takes precedence; eyes are open.

30 Eyes function inside womb; myelin forms to speed nerve signals.

32 For babies born at 32 weeks, survival rate approaches 98%.

34 Brain cortices are formed, implying ability to interpret and form memories; lungs are last organs to function at appropriate capacity.

38 Fetus is usually too large to move freely; number of neurons (not mass) is peaking; expected delivery date is now, after 266 days gestation or 280 days (40 weeks) after last menstrual period.

39–40 Approximately 12% of infants are born after their expected due date.

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Section 3.4 Environmental Influences in Prenatal Development

During weeks 28 through 40, the emphasis is on the maturing brain and further development of the body’s systems—respiratory, circulatory, digestive, and others. Coinciding with its place in evolutionary development, vision is the last sense to fully develop. While the eyes can blink and the fetus reacts to light shown through the abdomen, it is not until the 30th week that a pupillary reflex is consistently exhibited (Moore, Persaud, & Torchia, 2015). By that time the fetus has grown to about 75% of its normal birth length, but only to 40% of its weight. There- fore, much of the remaining time inside the womb is spent accumulating fat.

The latter part of weeks 26 through 40 is also notable for increased responsiveness to a num- ber of external sources. Fetuses respond favorably to familiar voices (DeCasper & Fifer, 1980; Fifer & Moon, 1989; Moon & Fifer, 1990), language (Moon, Cooper & Fifer, 1993), rhymes (DeCasper & Spence, 1986), and melodies (Cooper & Aslin, 1989). A number of studies have clearly demonstrated that learning and memory take place in utero, or before birth. See Chapter 7 for more information about cognitive development.

Section Review Beginning with the egg and sperm, trace the course of prenatal development through the embryonic period. Then outline various developmental processes that occur during the fetal period.

3.4 Environmental Influences in Prenatal Development A number of environmental influences that originate with the mother can affect the course of development. These include maternal nutrition and health, exposure to toxins, and health care access. Globally, there are major concerns over proper sanitation and the availability of a fresh water supply, which are often taken for granted in developed countries. By contrast, regular exercise and proper nutrition intake are generally positive influences. This section addresses how these issues affect prenatal development.

Nutrition The prenatal development depends entirely on the nutrients extracted from its mother, so there is sensitivity to the nutrition intake of the mother; when mothers are undernourished, the prenatal environment is too. Developing fetuses can adapt to undernutrition, but when they do, “it permanently alters the structure and function of the body” (Martin-Gronert & Ozanne, 2006, p. 779). Though undernutrition has declined over the past 20 years or so, it remains an entrenched problem in poor and middle-income countries, especially in southern Asia and Sub-Saharan Africa. These conditions contribute to large numbers of fetal and infant deaths and children who experience stunted growth, and they also carry forward to future generations among those who reach adulthood and have children of their own (Black et al., 2013; Walker, Chang, Wright, Osmond, & Grantham-McGregor, 2015).

Expectant mothers must have a balanced intake of macronutrients, vitamins, and minerals. They need to pay particular attention to their intake of lean proteins, which help to form

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Section 3.4 Environmental Influences in Prenatal Development

organs, as well as calcium, iron, and folate. Deficiencies in particular nutrients such as these can lead to specific problems. For instance, additional iron during pregnancy is needed to supply the fetus with adequate blood, and therefore oxygen. Otherwise there is increased risk for maternal anemia and of birth complications.

Pregnant women also need to make sure they consume adequate amounts of folate (or its synthetic form, folic acid). Folate can be found in dark green leafy vegetables, nuts, legumes, liver, and some fruits. If pregnant women fail to consume enough, their children are at risk for neural tube defects like spina bifida, in which the growing neural tube does not close completely. In many cases, the spinal cord will essentially grow outside the body. Because spina bifida has neither a localized occurrence nor a standard severity, it can cause a variety of neu- rological and orthopedic complica- tions. These can range from a barely noticeable curvature of the spine to severe malformations of the brain. In cases where the spinal cord is exposed, it must be surgically inserted into the

vertebral column in order to prevent infection. The surgery continues to be performed post- natally in many instances, but since 1997, it has also been performed prenatally, prior to 26 weeks gestation. Although the prenatal procedure shows significantly improved motor out- comes, there are associated maternal and fetal risks. For instance, there is a higher incidence of preterm delivery due to the necessary surgical rupture of the uterus (Adzick et al., 2011). There remains a tradeoff between improved neurological and physical development and the possibility of additional complications.

In 1996, Oman became the first country to mandate the addition of folic acid to fortified breads, cereals, grains, and other foods, specifically to reduce the incidence of spina bifida and other neural tube defects. The United States, Canada, and other countries soon followed. By the middle of 2015, 82 countries mandated some kind of fortification for wheat flour, and a number of others fortify maize and rice (Flour Fortification Initiative, 2015; Zimmerman, 2011). These simple changes to commercial foods have greatly reduced the incidence of neu- ral tube birth defects. In Mexico and South American countries, for instance, the incidence has declined between 33% and 59% (Rosenthal et al., 2014). Preliminary research suggests that use of folic acid supplements during early pregnancy may reduce the incidence of autism, perhaps by half (Surén et al., 2013).

One goal of the WIC program (Supplemental Nutrition Program for Women, Infants, and Chil- dren) in the United States is to increase nutrition among low-income pregnant women by providing healthy food. Though some data show that children born to women who take part in the WIC program are healthier and have developed better than those born to non-WIC mothers, other studies show mixed results (Jackson, 2015; Taylor & Niles, 2013).

Blend Images/Superstock

Consuming folate—which is found in dark green leafy vegetables, nuts, legumes, liver, and some fruit—can decrease the risk of defects like spina bifida.

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Section 3.4 Environmental Influences in Prenatal Development

While undernourished mothers are at risk for having babies with a multitude of potential problems, mothers who are severely overweight are an increasing concern as well. Higher rates of maternal obesity are associated with maternal and infant death, and they contribute to a higher incidence of birth defects. These findings are particularly alarming when coupled with the increasing obesity rate in the United States and elsewhere (Black et al., 2013; Crane, White, Murphy, Burrage, & Hutchens, 2009; Nicklas & Barbour, 2015; Yang & Colditz, 2015).

Exercise In addition to proper nutrition, pregnant women in good health are advised to exercise daily. Although there is no consensus on the ideal type, frequency, and intensity of exercise, research indicates that active women can maintain their pre-pregnancy training routines. For those who were previously unfit and sedentary, moderate exercise is generally recom- mended (Kehler & Heinrich, 2015; Nascimento, Surita, & Cecatti, 2012). Because of lifestyle changes and unfounded fears that exercise will harm the baby, up to half of women interrupt exercise regimens and only 1 in 6 engage in regular physical activity (Fieril, Olsen, Glantz, & Larsson, 2014; Nascimento, Surita, Godoy, Kasawara, & Morais, 2015). Current literature supports working out every day and light strength training. Exercise promotes the mainte- nance of proper weight and muscle tone (reducing the intensity of potential backaches); pre- vents or controls gestational diabetes; stimulates the circulatory and respiratory systems; and improves mood, energy, and sleep. There is substantial literature suggesting that exercise has no negative effect on fetal birth weight, size, or gestational age and can promote healthier outcomes in previously sedentary women (Binkley, Binkley, & Wise, 2015; Nascimento et al., 2012).

Mental Health In addition to the physical and psychosocial effects of nutrition and exercise, evidence indi- cates that the mother’s mental health affects development. A large Danish study reviewed 25 years of birth records in search of women who had been admitted to psychiatric hospitals (Webb et al., 2008). The researchers looked at 1.45 million birth records of children born in Denmark between 1973 and 1998 and found that birth defects increased significantly as a function of maternal admittance to psychiatric hospitals.

Not surprisingly, effects were especially strong for mothers who were admitted for schizo- phrenia or affective disorders (e.g., depression, bipolar disorder). (The same study also reported that the mental health of fathers did not have an effect on birth defects.) Note, how- ever, that mothers admitted to psychiatric facilities are also more likely to use prescription drugs for mental health treatment, as well as tobacco, drugs, and alcohol, all of which could be the cause of birth defects (Webb et al., 2008). In addition, children born to mothers with mental disorders such as schizophrenia may have been more strongly affected by prenatal nutritional deficiencies (Brown & Susser, 2008).

There is growing literature that there is a relationship between stress and infant outcomes. When we become stressed, the body releases a number of hormones to stimulate action (to get ready for “flight or fight”). This necessitates an increased flow of blood to the heart, mus- cles, and other organs and may temporarily deprive the fetus of its normal oxygen level. Hor- mones like cortisol cross the placenta and cause a rise in fetal heart rate (Monk et al., 2000, 2003). But because fetal experiences cannot be directly viewed or manipulated, the effects

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Section 3.4 Environmental Influences in Prenatal Development

of elevated cortisol levels is difficult to gauge. Although a few seconds of intense stress and anxiety may cause a temporary change in vital signs, it is likely that evolution would have accounted for short bursts of excitement. Indeed, women who experienced relatively acute stress in the wake of the 9/11 attacks on the World Trade Center had children who did not exhibit any adverse developmental effects (Endara et al., 2009).

On the other hand, it is well established that an association exists between maternal emotions and fetal behavior in the third trimester, with elevated cortisol levels suggesting broad effects on postnatal development (O’Connor, Monk, & Fitelson, 2014; Rash, Campbell, Letourneau, & Giesbrecht, 2015). Research indicates that women who experience prolonged stress and anxiety during early pregnancy have children who exhibit higher anxiety, poorer attention, decreased motor function, and poor self-regulatory behavior until at least elementary school; it is suggested that these consequences have lifelong implications (Cao, Laplante, Brunet, Ciampi, & King, 2014; Engel, Berkowitz, Wolff, & Yehuda, 2005; Fuller, 2014; Sandman, Davis, Buss, & Glynn, 2012). At the same time though, women who experience the most stress dur- ing pregnancy are also more likely to forsake healthy rest, exercise, and nutrition, which may independently affect developmental trajectories (DiPietro et al., 2004). Because of the appar- ent inconsistencies in the way that stress affects fetal outcomes, there is increasing attention directed to environmental stress that might prompt epigenetic changes in development (e.g., Lesseur, Paquette, & Marsit, 2014; Yehuda & Bierer, 2009; Yehuda et al., 2014).

Confounding factors in mothers’ postnatal behavior remains a factor in infant behavior as well. Women who experience more stress during pregnancy are probably less able to regulate their stress in general and are later less responsive to infant needs (Brand, Engel, Canfield, & Yehuda, 2006). Though a controlled study with mothers and children would be unethical, animal models convincingly demonstrate that early postnatal stress negatively affects later development (Modir, Salmani, Goudarzi, Lashkarboluki, & Abrari, 2014). Moreover, while research indicates that psychosocial stress during early pregnancy predicts slower mental development over the first postnatal year, several studies have found that elevated levels dur- ing the latter parts of pregnancy is associated with increased cognitive development during the first year (e.g., Davis & Sandman, 2010; Ellman et al., 2008). And a recent review finds that the majority of studies found no statistically significant effects between cortisol con- centrations among pregnant women and subsequent developmental outcomes in children (Zijlmans, Riksen-Walraven, & de Weerth, 2015). Clearly, the relationship between maternal stress and infant outcomes remains an important area for additional research.

Age As noted in Chapter 2, women approaching menopause have the most difficulty becoming pregnant. In addition to Down syndrome, advanced maternal age is associated with miscar- riage, stillbirths, and premature deliveries (Lampinen, Vehviläinen-Julkunen, & Kankkunen, 2009; Vincent-Rohfritsch, Le Ray, Anselem, Cabrol, & Goffinet, 2013). Nevertheless, the major- ity of older women give birth without complications. And perhaps because of the additional planning that often accompanies advanced maternal age, older mothers tend to have some advantages over their younger counterparts, including greater financial and social resources. As very young motherhood is associated with relatively poor parenting skills, mothers at the opposite spectrum are found to be more sensitive and responsive, contributing to develop- mental gains in their children (Bornstein, 2015). On average, young teenagers experience elevated rates of complications during pregnancy, labor, and delivery. They have higher rates

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Section 3.4 Environmental Influences in Prenatal Development

of stillbirths (deaths after the age of viability but before live birth) and premature deliveries. They are also the most likely to be economically disadvantaged and the least likely to pursue prenatal care, which complicates the findings (Substance Abuse and Mental Health Services Administration, 2014).

Prenatal Care and Socioeconomic Status Wide variations in education and income levels of expectant mothers lead to very different outcomes. Not surprisingly, lower quality prenatal care is associated with a number of health problems, including lower birth weights and poorer physical and cognitive development. Like other developmental issues, regional, racial, and ethnic differences do not tell the whole story. As Figure 3.9 shows, there are significant group differences in attention to prenatal health care, but socioeconomic status is usually a stronger indicator than race or ethnicity. That is, because of circumstances that include lack of transportation and knowledge, economically disadvantaged women in general are less likely to seek prenatal care. If certain minority groups are disproportionately poor, they will likely have disproportionate access to health care as well. One condition of the Patient Protection and Affordable Care Act (“Obamacare”) guarantees preventive health services for disadvantaged women, including maternity cover- age. This provision has the potential to improve reproductive health for minorities and low- income families through education and increased access to health care.

Figure 3.9: Percentage of mothers receiving late or no prenatal care, by race

and Hispanic origin, 2014

In aggregate, black, Hispanic, and Native American mothers are more than twice as likely as non- Hispanic whites to delay prenatal care until at least the third trimester.

Source: Child Trends. Used by permission.

Non-Hispanic white

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black

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Section 3.4 Environmental Influences in Prenatal Development

Threats to Prenatal Development Biology provides its own natural protection, but pregnant women must regard their bodies with some degree of caution. A teratogen refers to any unsafe environmental stimulus, includ- ing viruses and bacteria (e.g., sexually transmitted infections), prescription and nonprescrip- tion drugs, alcohol, tobacco, x-rays, pollution, exposure to chemicals, and even large doses of some essential vitamins. (See Table 3.4 for a list of some teratogens.) Although research is scant on the effect of a father’s contact with teratogens, studies have demonstrated genetic damage in sperm after prolonged exposure to such outside agents as operating room anes- thesia, pesticides, and radiation (Anderson, Schmid, & Baumgartner, 2014; Kaymak et al., 2012). Although research has also found a relationship between prenatal paternal variables and behavioral outcomes, it is extremely difficult to separate the effects of prenatal expo- sure (e.g., nicotine and other chemical residue) during pregnancy from postnatal factors (e.g., Langley, Heron, Smith, & Thapar, 2012).

On the other hand, fathers and other partners certainly have an effect on the prenatal envi- ronment. Second-hand smoke is potentially toxic; partners who cause undue stress on moth- ers may affect fetuses; toxins in the workplace have been known to affect sperm health and lead to birth defects; it appears that abuse of alcohol is associated with decreased sperm health (Dare, Noronha, Kusemiju, & Okanlawon, 2002; La Vignera, Condorelli, Balercia, Vic- ari, & Calogero, 2013; Shrivastava, Pekar, Grosser, Im, & Vigodner, 2010). Among pregnant women, though, it is clear that there is an association between environmental agents and various complications of pregnancy and development. Jim Wilson’s principles of teratogen sensitivity outlined over 50 years ago still apply today (Wilson, 1959):

• Susceptibility depends on the way in which teratogens interact with the environ- ment. Examples of these factors include the nature and strength of the toxic agent, the manner of exposure, and the rate and strength of transfer from the mother.

• Susceptibility varies with developmental stage. • Effects vary by the specific genotype of both mother and developing child. • There are four effects of teratogens: death, malformation, growth retardation, and

functional defect.

The degree of effect increases as dosage of the toxin increases. But alcohol is an especially powerful teratogen because it easily passes into the mother’s bloodstream and through to the fetus. Therefore, excessive drinking by mothers during pregnancy may result in fetal alco- hol spectrum disorders (FASD). Physical features of FASD include short stature, small head size, a characteristic absence or modification of the philtrum (the ridge between the upper lip and the nose), atypical features of the ears and eyes, and a curved fifth finger (Wattendorf & Muenke, 2005). Other physical manifestations can include poor balance and coordination, hyperactivity, and vision or hearing problems. In its severe form, called fetal alcohol syndrome, FASD always affects intellect by “altering the trajectory” of brain development (Treit et al., 2013). Typical consequences include problems with language development, poor attention and memory, and difficulty in tasks requiring critical thinking skills. FASD cannot be cured. Instead, treatment focuses on addressing characteristic behaviors and ensuring the availabil- ity of appropriate home and school resources.

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Section 3.4 Environmental Influences in Prenatal Development

Table 3.4: Selective teratogen sensitivity

Teratogen Potential effects

Tobacco Premature birth; small stature; respiratory problems; increased chance of miscarriage.1

Alcohol See text.

Radiation Cancer.2, 4

Retinoids (acne medication)

Large percentage (25–38%) exposed during first trimester show abnor- malities: excess fluid in the brain (hydrocephalus) and other brain defects, intellectual disability, physical abnormalities of face and limb, chronic skin lesions; cardiovascular and nervous system malformations. There is also an increased risk of miscarriage.3

Syphilis Prematurity; stillbirth or short lifespan.4

HIV Miscarriage, preterm birth, transmission of virus to fetus.5 When untreated, leads to a compromised immune system, opportunistic infections, neurocog- nitive impairment, and death.

Herpes (untreated) Preterm delivery; head and brain malformations.6, 7

Cocaine and Stimulants Higher risk of fetal malnutrition due to effect as an appetite suppressant. No convincing evidence of problems associated with mild intake of caffeine.8

Thalidomide Limb abnormalities; congenital heart disease.

Cannabinoids (marijuana) Inconclusive.

Notes: 1 Cornelius & Day, 2009; 2 Williams & Fletcher, 2010; 3 Malvasi, Tinelli, Buia, & De Luca, 2009; 4 Gilbert-Barness, 2010; 5 Joseph, Biodun, & Michael, 2011; 6 Li et al., 2014; 7 Corey & Wald, 2009; 8 Loomans et al., 2012.

Despite the increased attention surrounding marijuana in recent years, there is scant current evidence on the effects of marijuana use on birth outcomes and fetal development. A study of 12,825 women published in 1983 did not find any long-term consequences after extraneous variables were accounted for (Linn et al., 1983). In contrast, an Australian survey that asked 24,874 women about their use of cannabis and other illicit drugs during pregnancy found that cannabis use by pregnant women predicted low birth weight (2.5% of users) and pre- term births (1.5% of users) (Hayatbakhsh et al., 2012).

Though the volume of literature in this area continues to grow, most studies do not support an independent relationship between marijuana and negative birth outcomes, but they are beset by methodology problems. Most often, data are retrospectively culled from hospital records. In these instances, information is often incomplete and assessment methods vary. There are potentially strong confounding variables, like SES, health, and other drug use. Because most marijuana smokers also expose themselves to other teratogens, it is difficult to separate the negative effects of one substance from others (Hayatbakhsh et al., 2012). Even when infor- mation is gathered prospectively, it remains difficult to determine whether marijuana use predicts negative birth outcomes or if its use is a marker for an overall risky lifestyle (Dekker et al., 2012). Nevertheless, it appears intuitive that the hundreds of chemicals found in mari- juana (especially in the smokable form) should be avoided.

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Usually not susceptible to teratogens

Embryonic period (in weeks) Period of dividing

zygote, implantation, and gastrulation

Weeks 1 2 3 4 5 6 7 8 9 16 20–36 38

Major morphological abnormalities Functional defects and minor morphological abnormalities

Prenatal death

Palate

Teeth External genitals

External genitals

Central nervous system

Heart

Upper limbs

Lower limbs

Ears

Eyes

Teeth

Palate

External genitals

Leg LegArm Arm

Eye Eye Eye Ear Brain Brain Heart Heart

Ear

Heart

Fetal period (in weeks) – full term

Indicates common site of teratogen action

Section 3.4 Environmental Influences in Prenatal Development

Critical and Sensitive Periods of Development Teratogen sensitivity is largely dependent on dose, length of exposure, and period of develop- ment. Although there can be profound effects throughout pregnancy, specific consequences of teratogens vary by developmental stage. For instance, organ system development occurs dur- ing the embryonic period, when rapid growth of those systems takes place. Organogenesis will not take place outside of that specific time frame. When there is a defined period like organogenesis that results in specific consequences—both positive and negative—we say there is a critical period development. When a critical area of development has a less well- defined beginning and end point, it is alternatively referred to as a sensitive period.

Developmental outcomes are usually dependent as a combination of maturation and teratogens or matura- tion and nutrition (see Figure 3.10). For instance, infants whose mothers contract rubella (German mea- sles) during the first trimester are susceptible to being born deaf, blind, intellectually disabled, and with heart defects. By contrast, if pregnant mothers contract rubella after about the 20th week, there is little chance of negative effects on the fetus (Dontigny, Arsenault, & Martel, 2008).

Critical Thinking

Your friend just found out she is 3 weeks pregnant and is extremely worried about birth defects because she got drunk the weekend after she became pregnant. What advice would you give her?

Figure 3.10: Sensitivity to teratogens during various periods of pregnancy

Depending on the stage of prenatal growth, teratogens can have various effects on healthy development.

Source: From K. L. Moore and T. V. N. Persaud, Before We Are Born: Essentials of Embryology and Birth Defects, 7th ed., p. 313. Copyright . 2008. Reprinted by permission of Elsevier.

Usually not susceptible to teratogens

Embryonic period (in weeks) Period of dividing

zygote, implantation, and gastrulation

Weeks 1 2 3 4 5 6 7 8 9 16 20–36 38

Major morphological abnormalities Functional defects and minor morphological abnormalities

Prenatal death

Palate

Teeth External genitals

External genitals

Central nervous system

Heart

Upper limbs

Lower limbs

Ears

Eyes

Teeth

Palate

External genitals

Leg LegArm Arm

Eye Eye Eye Ear Brain Brain Heart Heart

Ear

Heart

Fetal period (in weeks) – full term

Indicates common site of teratogen action

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Section 3.5 Prenatal Tests

3.5 Prenatal Tests In developed countries, prenatal tests are available to monitor the growth and health of the fetus. Genetic risk factors, maternal age, and the mother’s personal and family medical history determine which of the most common tests might be used.

Ultrasound The most routine and least invasive test is ultrasound sonography. It uses high-frequency sound waves to create images. It is typically performed at around 7 weeks to confirm nor- mal gestation and a heartbeat, and is then performed periodically throughout the pregnancy. An early test can detect an ectopic pregnancy, a dangerous condition in which the embryo grows inside the fallopian tube rather than the uterus. In addition, abnormally high levels of fluid in a specific area at the back of the neck help detect Down syndrome and some genetic disorders. Physical abnormalities and multiple births can be detected, and at about 16 weeks the child’s sex is usually apparent.

Psychology in Action: Applying Research

The visual system provides an excellent example of a critical period of development. David Hubel and Torsten Wiesel (1970) won the Nobel Prize in Physiology or Medicine for their work with the visual system of cats, whose eyes are similar to those of humans. They found a number of specialized brain cells that react only to specific kinds of stimulation. For instance, when kittens were deprived of color or certain types of movement, they suffered irreversible damage to the visual system related to those deficits.

Their research also helped us to understand visual problems and how they might be treated. For instance, each human eye normally sends signals to the brain from a slightly different loca- tion (binocular disparity), allowing us to synthesize input and coordinate depth perception. When children have strabismus (are “cross-eyed”), binocular disparity and depth perception suffer because eye movements are not coordinated; one eye is usually dominant while input from the other is neglected. When the brain is deprived of one eye’s input during infancy and early childhood, the dominant eye performs most of the visual tasks. As a result, the part of the brain that is supposed to receive signals from the weaker eye does not develop properly, which leads to permanent deficits in depth perception. If strabismus, which occurs in 2–5% of normal births, is not corrected through surgery or eye exercises during early childhood, individuals will never gain proper depth perception (Vaegan & Taylor, 1979). Like other criti- cal periods of development, specific kinds of deprivation therefore predict specific kinds of deficits.

Section Review Summarize the threats to prenatal development, and identify when such threats may have negative effects on the fetus.

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Section 3.5 Prenatal Tests

Chorionic Villus Sampling Chorionic villus sampling (CVS) is more invasive than ultrasound. It is performed when family history or maternal age indicates a higher risk pregnancy. It is usually done between the 10th and 13th weeks. CVS removes a sample of chorionic villi, which are cells contained in the placenta at the point where it attaches to the uterine wall. The cells are then analyzed for chromosomal and genetic abnormalities. The principal advantage of CVS is that it can be performed earlier than amniocentesis, which is discussed next.

Amniocentesis As the fetus grows, cells are shed into the amniotic sac. Amniocentesis involves drawing amniotic fluid from the pro- tective (amniotic) sac that surrounds the fetus, and analyzing the cells. Like CVS, it is usually performed when there is a high risk of fetal complications (family history, maternal age). Like CVS, amniocentesis is an invasive procedure. Although negative outcomes are rare, there is a risk of miscarriage due to resultant infections or the premature onset of the birthing process. There is also a chance the needle may contact the fetus, but with simultaneous sonog- raphy the incidence is rare.

Blood Tests Advancements in testing also allow us to screen for chromosomal abnormalities by a simple blood test. Regardless of age or other risk factors, the American Congress of Obstetricians and Gynecologists recommend that during the first trimester, women should be tested for pregnancy-associated plasma protein (PAPP-A), which is produced by the placenta (ACOG, 2007). Abnormal levels can reliably detect Down syndrome and other chromosomal abnor- malities with about 85% accuracy. Early testing for the hormone human chorionic gonadotro- pin (hCG) is part of the screening as well. This test helps to diagnose ectopic pregnancies and risk factors for possible miscarriages. Together, these two tests allow women to make more informed decisions before having more invasive (and reliable) amniocentesis and CVS.

Between the 15th and 20th weeks (ideally between weeks 16 and 18) the first trimester tests are repeated and additional screening is completed for alpha-fetoprotein (AFP), a protein nor- mally produced by the fetal liver, estriol, a form of estrogen, and inhibin-A, a hormone that is found in higher concentrations when women are carrying a fetus with Down syndrome. These additional screenings during the second trimester also help to assess additional risk factors for miscarriage and neural tube defects, such as spina bifida.

Burger/Phanie/Superstock

During amniocentesis, a doctor will use sonography to avoid coming into contact with the fetus.

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Section 3.6 Infertility and Reproductive Choice

3.6 Infertility and Reproductive Choice Though advanced technology is available to monitor early development, sometimes simply becoming pregnant is difficult. In the United States, primary infertility is usually defined when, over a 12-month period, a couple that is not using contraceptives is unable to con- ceive their first child. Approximately 10% of couples overall fit this definition, but it varies greatly by age. One frequently cited study recorded fertility rates in the 1950s, employing a sample that had never used any kind of birth control. It was found that only 7% of couples were infertile by age 30, but that figure rose to 33% by age 40, and 87% by age 45 (Tietze, 1957). Over the last several decades these rates have generally remained quite consistent worldwide. However, for unknown reasons, the United States, South Asia, and Sub-Saharan Africa have shown recent decreases in rates of infertility (Chandra, Copen, National Center for Health Statistics, & Stephen, 2014; Marsh & Ronner, 1996; Mascarenhas, Flaxman, Boema, Vanderpoel, & Stevens, 2012).

Causes of male infertility include obstructions in the reproductive tract; low sperm count; and lack of sperm motility (ability to move), making sperm unable to reach the fallopian tube. Though women are born with all of their eggs, they may have difficulty ovulating, obstruc- tions in their fallopian tubes, or a uterine problem that prevents implantation. A comprehen- sive analysis in the United Kingdom found that about 30% of infertility was attributable to men and about 30% to women. The remaining causes either were attributed to dual compli- cations or remained unexplained. Smoking, obesity, and excessive drinking reduced fertility in both sexes (Expert Group on Commissioning NHS Infertility Provision, 2009).

Secondary Infertility Secondary infertility is a phenom- enon that describes couples who have had one child but are unable to conceive again. Like other social issues, studying secondary infertility can be problem- atic as there is not one standard defi- nition. For instance, some have argued that because of China’s “one child” policy, which was eased at the end of 2013 and abolished at the end of 2015, their rate of secondary infertility was virtually zero (Boivin, Bunting, Collins, & Nygren, 2007; Larsen, 2005; Mas- carenhas, Cheung, Mathers, & Stevens, 2012). When few couples desire to have a second child, documented cases of secondary infertility are rare.

Florian Kopp/imagebro / imageBROKER/Superstock

In Pakistan, women who experience secondary infertility face acute stigmas that can result in both social and health consequences.

Section Review Describe the common prenatal tests, the purpose of each, and when they are administered.

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Section 3.6 Infertility and Reproductive Choice

Though it is estimated that half of infertility cases originate with men, women are often viewed as solely responsible in many of the countries where secondary infertility is highest. Infertility among women throughout the African continent is a major cause of divorce (Dyer, Hoffman, & van der Spuy, 2002). In Pakistan, infertile women are subject to abuse and threats of divorce. In one survey, over half of Pakistani respondents reported that female infertility is sufficient reason for a man to take a second wife. Many wives agree, and others are forced to comply (Ali et al., 2011). As such, these women are acutely stigmatized, and the stigma carries with it large psychosocial and health consequences. Secondary infertility is particu- larly prevalent among the poor in southern Asia, Latin America, and Africa, affecting between 15% and 25% of women over the age of 25. However, in the Infertility Belt that stretches across central and southern Africa, the rate of secondary infertility is the highest in the world, exceeding 30%. This rate is largely the result of women marrying at an early age, and then contracting a sexually transmitted disease. After giving birth to one child, the disease incu- bates long enough for it to cause permanent reproductive damage in both men and women. In contrast, the secondary infertility rate is less than 8% in high-income countries (Mascarenhas et al., 2012).

Choices in Reproduction Modern research and technology have helped increase the chances of having a successful pregnancy among couples and individuals who could not have conceived a century ago. In addition, the social climate has changed, and a greater number of older couples and gay and lesbian couples are interested in having children. Couples can turn to adoption, surrogate motherhood, hormonal treatments, or procedures known as assisted reproductive tech- nologies (ART).

Assisted Reproductive Technologies To increase the chances of pregnancy through intercourse, hormones can sometimes be administered to stimulate ovulation in women or increase the sperm count in men. Other times, surgery is indicated in order to remove blockages. If surgery or hormone treatments are either ineffective or not indicated, couples can consider in vitro fertilization (IVF). In this procedure, an egg and a sperm are combined in a laboratory. The zygote is then implanted in the woman’s uterus. In the case of a gay male couple, a surrogate mother would also be employed.

Sometimes the eggs and sperm are injected directly into the fallopian tube instead of being fertilized in a lab. This procedure is called gamete intrafallopian transfer (GIFT). When the fertilized egg is implanted in the fallopian tube, it is called zygote intrafallopian transfer (ZIFT). In 2012 there were 157,662 ART pro- cedures (Centers for Disease Control and Prevention, 2014a). Overall, about 36% of ART procedures result in pregnancy and about 29% result in live births, repre- senting a failure rate of about 18% after pregnancy. But the success of ART transfers varies by type of procedure and maternal age, including whether the mother is using her own eggs or those of a donor. For instance, when women aged 45 and older use their own eggs,

Critical Thinking

As reproductive technology continues to advance, procedures undoubtedly will be more successful in allowing older women to carry children to term. Under what con- ditions, if any, should restrictions be made on who can receive ART? Would it make a difference if older women were employed only as surrogate mothers carrying chil- dren for others?

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28 30 32 34 36

Age

38 40 42 44 46 4826 0

P e rc

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Donor eggs

Own eggs

Section 3.6 Infertility and Reproductive Choice

successful uterine implantation and live birth is rare, as shown in Figure 3.11. Studies show that the aging effects are due primarily to ovaries and eggs, not the uterus. Among older women who use donor eggs, implantation is nearly as successful as among younger women. In addition, there are no developmental differences between full-term infants born to ART recipients or couples who conceived naturally (van Beijsterveldt, Bartels, & Boomsma, 2011)

Figure 3.11: Effect of advancing female age on success of IVF

Advancing age is a significant factor in the success of IVF, when a woman uses her own eggs. When women use donor eggs from younger mothers, there is little drop off in success of live births.

Source: Adapted from ART 2010 National Summary. “Percentages of Transfers That Resulted in Live Births for ART Cycles Using Fresh Embryos from Own Eggs and ART Cycles Using Fresh Embryos from Donor Eggs, by Age of Woman, 2010.” Fig. 44. Centers for Disease Control.

28 30 32 34 36

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38 40 42 44 46 4826 0

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Adoption When couples are in danger of a high-risk pregnancy or are unable to conceive, another alter- native is adoption. Although the number of children who are adopted in the United States has been increasing, the percentage of adults who adopt has been decreasing. This information implies that a smaller pool of parents is adopting larger numbers of children (Child Welfare Information Gateway, 2011). Whether children are adopted by gay, lesbian, or heterosexual parents, most studies find that adopted children do equally well (Biblarz & Stacey, 2010). In general, adopted children tend to have more problematic behaviors and have poorer cogni- tive functioning; increasing age at adoption is associated with increased problems. However, these findings are always confounded because of the high percentage of adopted children who are maltreated, come from unstable families, or were medically neglected, including those whose mothers received poor prenatal care (Beckett et al., 2006; Van IJzendoorn, Juffer,

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Summary & Resources

Chapter Summary Modern research has uncovered a great deal about genetic foundations but has also informed us about all that is yet to be discovered. In contrast, scientists know much more about biological beginnings. At any particular time during pregnancy, we have a fairly good idea of the processes that are under way. These processes must be protected through proper nutrition, exercise, and the avoidance of teratogens. In addition, specific prenatal tests should be a part of every pregnancy. Various combinations of factors are responsible for couples having difficulty conceiving, many of which remain a mystery. However, assisted reproductive technologies exist that allow modern couples additional choices in reproduc- tion. In the next chapter we will consider the birth process and explore the beginnings of postnatal development.

Summary of Key Concepts Genetic Foundations

• Genetics provides the foundation for the growth of living organisms. The genetic code for humans is found in strands of DNA that are contained in chromosomes.

• Genes, located on segments of DNA, contain the specific hereditary information that is transferred from one generation to the next.

• The Human Genome Project discovered that genes do not function independently. There is not often a one-to-one relationship between genes and specific traits. Genes usually interact with other genes and with the environment, turning on and off depending on biological and environmental circumstances.

• Sandra Scarr and her colleagues describe three patterns of genotype-environmental interactions: passive genotype-environment effects occur when children have no control over the relationship between their genes and the environment; evocative genotype-environment effects occur when genetic predispositions evoke responses from others; active (niche-picking) genotype-environment effects occur when chil- dren pursue an available niche depending on a particular genotype.

& Poelhuis, 2005). International adoptions have an especially high percentage of children who were medically or emotionally neglected or whose developmental history is unknown (Howard & John, 2013; Nickman et al., 2005). Regardless of any specific circumstances of a child’s history, the most important factors in a successful transition include parental prepara- tion and a lack of family conflict. Sensitive, responsive parents in general are strong predic- tors of cognitive and social outcomes in children and contribute to successful relationships in adulthood (Goldberg & Smith, 2013; Koh & Rueter, 2011).

Section Review Explain some of the causes of infertility and when an individual or a couple might use repro- ductive technology. Explain three ART procedures.

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Summary & Resources

Genetic Variations

• Gene mutations, the cornerstone of evolutionary adaptation, are sometimes benefi- cial by aiding survival and at other times are harmful.

• Abnormalities sometimes occur because of specific combinations of pairs of alleles; other times there are distinct chromosomal changes.

• X-linked variations affect significantly more males than females because of the struc- ture of chromosomes and the way that genetic information is transmitted.

• Down syndrome, or Trisomy 21, is a developmental disorder characterized by mod- erate to severe deficits in physical and cognitive functioning. It is the most common chromosomal abnormality.

Conception and Prenatal Development

• Scientists differentiate among germinal, embryonic, and fetal periods, while doctors and the public more commonly refer to trimesters. Both methods of organization are helpful.

Conception and Germinal Period

• Conception takes place when a male sperm fertilizes a female egg. The resulting zygote travels through the fallopian tube and is implanted in the uterus where it becomes an embryo.

• The germinal period, or period of the zygote, lasts the first 14 days until the embryo is implanted in the uterine wall.

Embryonic Period

• The embryonic period lasts from 2 to 8 weeks when the fetal period begins. • It is characterized by the primitive differentiation of structures, including organs

and parts of the brain.

Fetal Period

• The fetal period encompasses part of the first trimester of development and the entire second and third trimesters.

• Lanugo and vernix help to protect the fetus during the prenatal period and aid in the delivery process.

• Sex organs develop near the end of the first trimester. • Organs begin to function at the beginning of the second trimester. This period also

marks the age of viability, when fetuses can survive outside the womb. Children born near this age always need medical support in order to survive.

• Surfactant therapy is generally indicated prior to 26 weeks gestation. This treatment increases the risk of postnatal complications.

• Development in the last trimester centers on the maturing brain and the body’s systems—respiratory, circulatory, digestive, and others.

• During the third trimester, fetuses become responsive to a number of external stimuli.

Environmental Influences in Prenatal Development

• Prenatal influences vary widely by culture and individuals. • The prenatal environment must be protected through proper nutrition, exercise, and

the avoidance of teratogens.

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Summary & Resources

• It is important for pregnant women to consume the right balance of nutrients. A singular deficiency in folate, for instance, is known to cause neural tube deficits.

• Exercise is recommended for all healthy, pregnant women. Moderate (for previously sedentary) and vigorous (for previously active) women appears to have no nega- tive effects on fetal birth weight, size, or gestational age and can promote healthier outcomes.

• It appears that there is a relationship between stress and infant outcomes, but evi- dence is equivocal.

• Teratogen sensitivity is largely dependent on dose, length of exposure, and the developmental stage during which exposure occurred.

• Critical periods denote the time when specific growth occurs. Actions by the mother (and to a lesser extent) others will either promote or interfere with the acquisition of skills and physical growth.

• Ideally, prospective mothers should get regular checkups and be informed about proper nutrition and potential teratogens.

• Both ends of the age spectrum are associated with pregnancy and birth complica- tions. Young teens are more likely to be economically and socially disadvantaged while older mothers appear to have relatively superior parenting skills.

Prenatal Tests

• Ultrasound sonography is a simple, non-invasive prenatal test that uses high- frequency sound waves to create images.

• Chorionic villus sampling is performed when family history or maternal age indi- cates a higher risk pregnancy. In this procedure, cells in the placenta are removed and analyzed.

• Amniocentesis involves analyzing fluid that is drawn from the amniotic sac. • Regardless of age or other risk factors, it is recommended that women be tested for

various proteins and hormones that can potentially identify negative birth complica- tions and genetic variability.

Infertility and Reproductive Choice

• In primary infertility, the maternal age is often the most important factor; secondary infertility is quite prevalent within the Infertility Belt, probably due to widespread sexually transmitted diseases.

• Modern technology has increased reproductive options for millions of individuals and couples throughout the world. Common methods include IVF, GIFT, and ZIFT.

Critical Thinking and Discussion Questions

1. There are few teratogenic effects during the period of the zygote. Explain why this might be an evolutionary adaptation.

2. Explain the relationship between thalidomide, a teratogen that was at one time pre- scribed for morning sickness, and the resultant birth defects of limbs. That is, why do “thalidomide babies” specifically have malformations of arms and legs?

3. We often hear of children of professional athletes who grow up to become superior athletes themselves. Explain how a gene-environment interaction might be passive, active, or evocative in leading the next generation of athletes.

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Summary & Resources

4. Under what circumstances would it be acceptable to terminate a pregnancy based on sex? Alternatively, as technology progresses, under what circumstances would it be acceptable to choose the sex of a child? What about different traits, such as eye color, intelligence, or artistic ability?

5. Under what scientific circumstances would you view the age of viability differently than it is currently conceptualized?

6. ZIFT and GIFT have success rates that are significantly less than 50%. Would you consider them experimental procedures?

7. ZIFT and GIFT procedures cost more than $10,000, and sometimes up to five times that amount. Under what circumstances (if any) should health insurance or the Affordable Care Act (“Obamacare”) cover the costs? (Remember, it is not “free” money, everyone eventually pays for healthcare for all.)

Additional Resources Web Resources

• American College of Obstetricians and Gynecologists, guidelines for exercise http://www.acog.org/Patients/FAQs/Exercise-During-Pregnancy

• Cystic Fibrosis Foundation https://www.cff.org/

• FRAXA Research Foundation http://www.fraxa.org/

• Monroe Carell Jr. Children’s Hospital at Vanderbilt, Pioneers of prenatal surgery for spina bifida https://www.childrenshospital.vanderbilt.org/fetalsurgery

• National Down Syndrome Society http://www.ndss.org/

• National Tay-Sachs & Allied Diseases Association http://www.ntsad.org/

• Sickle Cell Disease Association of America (SCDAA) http://www.sicklecelldisease.org/index.cfm?page=contact-scdaa

• Turner Syndrome Foundation http://www.turnersyndromefoundation.org/

• United States Department of Agriculture, Health and nutrition information for preg- nant women http://www.choosemyplate.gov/moms-pregnancy-breastfeeding

Further Research

• Adzick, N. S., Thom, E. A., Spong, C. Y., Brock, J. W., Burrows, P. K., Johnson, M. P., . . . Farmer, D. L. (2011). A randomized trial of prenatal versus postnatal repair of myelo- meningocele. New England Journal of Medicine 364(11), 993–1004. Retrieved from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3770179/

• International Human Genome Sequencing Consortium. (2004). Finishing the euchromatic sequence of the human genome. Nature, 431, 931–845. doi:10.1038/ nature03001 Retrieved from http://www.nature.com/nature/journal/v431/n7011/ pdf/nature03001.pdf

• National Partnership for Women and Families. (2014). Why the Affordable Care Act matters for women: Health insurance coverage for lower- and moderate-income pregnant women. Fact Sheet. Retrieved from http://www.nationalpartnership.org/ research-library/health-care/lower-and-moderate-income-pregnant-women.pdf

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http://www.acog.org/Patients/FAQs/Exercise-During-Pregnancy

https://www.cff.org/

http://www.fraxa.org/

https://www.childrenshospital.vanderbilt.org/fetalsurgery

http://www.ndss.org/

http://www.ntsad.org/

http://www.sicklecelldisease.org/index.cfm?page=contact-scdaa

http://www.turnersyndromefoundation.org/

http://www.choosemyplate.gov/moms-pregnancy-breastfeeding

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3770179/

http://www.nature.com/nature/journal/v431/n7011/pdf/nature03001.pdf

http://www.nationalpartnership.org/research-library/health-care/lower-and-moderate-income-pregnant-women.pdf

Summary & Resources

Key Terms active (niche-picking) genotype- environment effects Children’s seeking of environments that are promoted by their hereditary endowment.

age of viability The earliest age at which a fetus can survive outside the womb.

allele One member of a pair of genes; composed of DNA that carries hereditary information.

amniocentesis A prenatal test of cells from the amniotic fluid that can be analyzed for genetic abnormalities.

amniotic fluid The liquid that nourishes and protects the developing fetus during pregnancy.

assisted reproductive technologies (ART) A general term that refers to reproductive processes achieved by artificial means.

chorionic villus sampling (CVS) An early prenatal test that samples fetal cells that can be analyzed for genetic abnormalities.

chromosome A structure within a cell that contains a configuration of DNA, where genetic information is contained.

conception The moment that a sperm fer- tilizes an egg to form a zygote.

critical period A time during which envi- ronmental influences have the greatest impact on development.

cystic fibrosis An inherited genetic disease characterized by respiratory and digestive problems.

DNA (deoxyribonucleic acid) A molecule that contains genetic instructions that prescribe the unfolding of developmental processes.

dominant (allele) An allele that is expressed in a phenotype regardless of its corresponding allele.

Down syndrome The most frequent cause of intellectual disabilities; identified by three chromosomes on the 21st pair.

ectopic pregnancy A dangerous condition in which the embryo does not implant in the uterus and instead begins growing in the fallopian tube.

embryo This refers to the fertilized egg that is implanted in the uterine wall following the period of the zygote. The embryonic stage lasts from about the second week to about week 8.

embryonic period Generally refers to the period of development from the beginning of week 3 until the end of week 8.

evocative genotype-environment effects Children’s evoking of responses from the environment because of hereditary influences.

fallopian tube The duct that leads the ova from the ovaries to the uterus.

fetal alcohol spectrum disorders (FASD) A group of developmental disorders caused by mothers drinking excessive alco- hol during pregnancy.

fetal period The gestational period that extends from week 9 until birth.

fetus The developing organism from about week 9 until birth.

folate An essential vitamin necessary for the manufacture and repair of DNA.

folic acid The synthetic form of folate.

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Summary & Resources

Fragile X syndrome A genetic disorder that is a leading cause of inherited intellectual disabilities.

gamete intrafallopian transfer (GIFT) A reproductive procedure that transfers sperm and ova into a fallopian tube.

gametes Reproductive cells (sperm, ova).

gene mutations Changes in the DNA sequence of genes.

genes Units of DNA that carry hereditary information.

genotype The genetic code for certain traits of an organism.

germinal period (or period of the zygote) The first 2 weeks after fertilization, when the zygote travels through the fallo- pian tube and is implanted in the uterus.

gestational period Time of prenatal growth. In humans, 266 days from date of conception.

infant mortality The death of an infant before the age of 1 year.

Infertility Belt An area across central and southern Africa where secondary infertility rates are the highest in the world.

intersex A disorder of sexual develop- ment in which there is an inconsistency between sex chromosomes and anatomical development.

in utero Before birth.

in vitro fertilization (IVF) A procedure in which an egg and a sperm are combined in a laboratory. The zygote can then be implanted.

Klinefelter’s syndrome A genetic disorder in which males have at least one extra X sex chromosome.

miscarriage An uncompleted pregnancy.

nucleus The central structure of a cell.

organogenesis Early in utero organ devel- opment that occurs during the embryonic period.

ovaries Female reproductive organs that contain ova (eggs).

ovum The mother’s egg (reproductive) cell. Plural: ova.

passive genotype-environment effects Children’s genes being promoted by the actions of parents and other adults who choose the tasks and environments to which children will be exposed.

phenotype The observable expression of a genotype.

placenta Tissue that connects the devel- oping fetus to the mother and allows the exchange of waste, nutrients, and gases.

primary infertility Occurs when a couple cannot conceive after having regular inter- course over 24 or, alternatively, 12 months.

recessive (allele) An allele that usually needs to combine with a corresponding recessive allele in order to be expressed in a phenotype.

secondary infertility Occurs when couples who have had one child are unable to con- ceive again.

secondary sex characteristics Character- istics of males and females that are visible beginning with puberty.

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Summary & Resources

sex chromosomes The chromosomes that determine whether an organism is male or female.

sickle cell disease A genetic disorder that causes the body to make sickle-shaped red blood cells. The cells do not carry sufficient amounts of oxygen to the body, which often results in anemia.

sperm A male’s reproductive cell.

spina bifida A neural tube defect, in which the neural tube does not close completely.

surfactant A substance contained in the lungs that keeps them from collapsing, and allows exchange of gases.

Tay-Sachs disease A genetic neurological disorder that results in the early death of children.

teratogen A substance that interferes with the normal development of an embryo or a fetus.

testes The male glands responsible for manufacturing the male reproductive cells (see sperm). Singular: testicle.

trimesters Three approximately equal terms of 13 weeks during pregnancy.

Triple X A genetic disorder characterized by the presence of an additional X chromo- some in a female.

Trisomy 21 Down syndrome.

Turner syndrome A genetic disorder marked by a missing X sex chromosome.

ultrasound sonography A prenatal test that provides a visual image of the fetus.

umbilical cord A structure that attaches the placenta to the fetus at the “belly button.”

uterus The womb in which the fetus devel- ops during gestation.

X-linked variation When an abnormal gene is carried on only one sex chromosome.

XYY A genetic disorder characterized by an extra Y chromosome in males.

zygote A fertilized egg. After about 2 weeks, the zygote becomes an embryo.

zygote intrafallopian transfer (ZIFT) A reproductive procedure that transfers at least one fertilized egg into the fallopian tube.

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