The early days of prenatal life place the developing person on a path toward health and success—or not. Fortunately, resilience is apparent from the beginning; healthy newborns are the norm, not the exception.

We now look at specific problems that may occur and how to prevent or minimize them. Always remember dynamic systems—every hazard is affected by dozens of factors.

Perhaps half of all zygotes have serious abnormalities of their chromosomes or genes. Usually they never grow or implant. However, some such zygotes survive, grow, develop, and are born to live a satisfying life.

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NOT EXACTLY 46 As you know, each sperm or ovum usually has 23 chromosomes, creating a zygote with 46 chromosomes and eventually a person. However, cells do not always split exactly in half to make gametes, partly because of the age of the parents—particularly the mother. About once in about every 200 births is a baby born with 45, 47, or, rarely, 48 or 49 chromosomes.

If an entire chromosome is missing or added, that leads to a recognizable syndrome, a cluster of distinct characteristics that tend to occur together. Usually the cause is three chromosomes at a particular location instead of the usual two (a condition called a trisomy).

The most common survivor with 47 chromosomes is a person with Down syndrome. This syndrome is also called trisomy-21 because the person has three copies of chromosome 21. In the United States, 6,000 babies per year are born with Down syndrome.

Some 300 distinct characteristics may result from that third chromosome 21, usually including a thick tongue, round face, slanted eyes, hearing problems, heart abnormalities, muscle weakness, and short stature. Intellectual development is often slow. Family context, educational efforts, and possibly medication can decrease the harm (Kuehn, 2011).

The other common miscount involves the sex chromosomes. Every human has at least 44 autosomes and one X chromosome; an embryo cannot develop without those 45. However, about 1 in every 500 infants is born with only one sex chromosome (no Y) or with three or more (not just two). Having an odd number of sex chromosomes impairs cognition and sexual maturation. Specifics depend on exactly which chromosomes are at that 23rd site (XYY, XXX, XO, and so on) as well as epigenetics (Hong & Reiss, 2014).

GENE DISORDERS Everyone carries alleles that could produce serious diseases or handicaps in the next generation. The phenotype is affected only when the inherited gene is dominant or when both parents carry the same recessive gene and the zygote inherits the harmful gene from both, or when a particular combination of genes from both parents triggers a problem.

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Serious dominant disorders are rare, because those who have them rarely live to become parents. However, a few dominant disorders do not affect the person until adulthood.

Adult onset occurs with Huntington’s disease, a fatal central nervous system disorder caused by a copy number variation—more than 35 repetitions of a particular set of three base pairs. The symptoms first appear when a person could have had many children, as did the original Mr. Huntington. Half of them inherited his dominant gene.

Recessive diseases are more common, because people are often unaware that they are carriers, and being a carrier may confer some benefit. About 1 in 12 North American men and women carries an allele for cystic fibrosis, thalassemia, or sickle-cell disease.

Consider the most studied example: sickle-cell disease. Carriers die less often from malaria, so the gene protected more people (the carriers) than it killed. If a couple in a malaria prone region were both carriers and had four children, odds are that one would die of sickle-cell disease, one would not be a carrier and might die of malaria, but two would be carriers, protected against a common, fatal disease. They would survive, become parents, and thus the recessive trait would spread.

Almost every genetic disease is more common in one group than in another (Weiss & Koepsell, 2014). About 11 percent of Americans with African ancestors are carriers of the sickle-cell gene; cystic fibrosis is more common among Americans with ancestors from northern Europe because carriers may have been protected from cholera. Dark skin is protective against skin cancer, and light skin allows more vitamin D to be absorbed from the sun—a benefit if sunlight is scarce.

Each nation targets the genetic disorders that are common among its citizens. In the United States, people with cystic fibrosis or sickle-cell anemia can now live normal lives. In Cyprus and southern China, the focus is on thalassemia (Lo, 2015).

Some recessive conditions are X-linked, including fragile X syndrome, which is caused by more than 200 repetitions on one gene (Plomin et al., 2013). The cognitive deficits caused by fragile X are the most common form of inherited intellectual disability (many other forms, such as trisomy-21, are not usually inherited).

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The early days of life place the developing fetus on the path toward health and success—or not. Most newborns are quite healthy, but if something is amiss, it is often part of a cascade that may become overwhelming (Rossignol et al., 2014).

The cascade may begin before a woman realizes she is pregnant, as many toxins, illnesses, and experiences can cause harm early in pregnancy. Every week, scientists discover an unexpected teratogen, which is anything—drugs, viruses, pollutants, malnutrition, stress, and more—that increases the risk of prenatal abnormalities and birth complications.

Many teratogens cause no physical defects but affect the brain, making a child hyperactive, antisocial, or learning-disabled. These are behavioral teratogens. One of my students wrote:

I was nine years old when my mother announced she was pregnant. I was the one who was most excited. . . . My mother was a heavy smoker, Colt 45 beer drinker and a strong caffeine coffee drinker.

One day my mother was sitting at the dining room table smoking cigarettes one after the other. I asked, “Isn’t smoking bad for the baby?” She made a face and said, “Yes, so what?”

I asked, “So why are you doing it?”

She said, “I don’t know.”. . .

During this time I was in the fifth grade and we saw a film about birth defects. My biggest fear was that my mother was going to give birth to a fetal alcohol syndrome (FAS) infant. . . . My baby brother was born right on schedule. The doctors claimed a healthy newborn. . . . Once I heard healthy, I thought everything was going to be fine. I was wrong, then again I was just a child. . . .

My baby brother never showed any interest in toys. . . . [H]e just cannot get the right words out of his mouth. . . . [H]e has no common sense. . . .

Why hurt those who cannot defend themselves?

[J., personal communication]

As you remember from Chapter 1, one case proves nothing. J. blames her mother, although genes, postnatal experiences, and lack of preventive information and services may be part of the cascade as well. Nonetheless, J. rightly wonders why her mother took the risk.

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EVALUATING RISKS Risk analysis is crucial in human development (Sheeran et al., 2014). Although all teratogens increase the risk, none always causes damage. Risk analysis involves probabilities, not certainties (Aven, 2011).

For both risk and protection, timing may be crucial. The first days and weeks after conception (the germinal and embryonic periods) are the critical period for body formation, and the final months are important for body weight. Health during the entire fetal period affects the brain (see Figure 2.7).

Obstetricians recommend that before pregnancy occurs, women should avoid drugs (especially alcohol), supplement a balanced diet with extra folic acid and iron, update their immunizations, and gain or lose weight if needed. Indeed, preconception health is at least as important as postconception health (see Table 2.4).

A second crucial factor is the dose and/or frequency of exposure. Some teratogens have a threshold effect; they are harmless until exposure reaches a certain level, at which point they “cross the threshold” and become damaging. This threshold is not a fixed boundary: Dose, timing, frequency, and other teratogens affect when the threshold is crossed (O’Leary et al., 2010).

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Data from Bombard et al., 2013; MMWR, July 20, 2012; Brody, 2013; Mosher et al., 2012; U.S. Department of Health and Human Services, December, 2012.

Experts rarely specify thresholds, partly because one teratogen may affect the threshold of another. Alcohol, tobacco, and marijuana are more teratogenic, with a lower threshold for each, when all three are combined.

Is there a safe dose for psychoactive drugs? Perhaps, but, as my student asked, why risk it? Consider alcohol. During the early weeks, heavy drinking can cause fetal alcohol syndrome (FAS), distorting facial features (especially the eyes, ears, and upper lip). Later in pregnancy, alcohol is a behavioral teratogen. One longitudinal study of 7-year-olds found that in the last trimester binge drinking was most harmful to the brain (Niclasen et al., 2014).

Genes are a third factor that influences the effects of teratogens. When a woman carrying dizygotic twins drinks alcohol, for example, the twins’ blood alcohol levels are equal; yet one twin may be protected because alleles for the enzyme that metabolizes alcohol may differ. Differential susceptibility is evident (McCarthy & Eberhart, 2014).

The Y chromosome makes male fetuses more vulnerable. They are more likely to be spontaneously aborted or stillborn and more likely to be harmed by teratogens than female fetuses are. This is true overall, but the male/female hazard rate differs from one teratogen to another (Lewis & Kestler, 2012).

Maternal genes may be important during pregnancy. One allele results in low levels of folic acid in a woman’s bloodstream. Her deficiency, via the placenta, affects the embryo, which may develop neural-tube defects—either spina bifida, in which the tail of the spine is not enclosed properly (enclosure normally occurs at about week 7), or anencephaly, in which part of the brain is missing.

Neural-tube defects are more common among people from Ireland, England, and Egypt and rare among Asians and sub-Saharan Africans. Rates are down among Americans because folic acid is now a required additive in cereal and bread.

MAKING PREDICTIONS Results of teratogenic exposure cannot be predicted precisely in individual cases, although impact can be measured for the population, as evident with neural-tube defects. Much is also known about how individuals can reduce the risks.

General health is protective. Women who maintain good nutrition and avoid drugs and teratogenic chemicals (often in pesticides, cleaning fluids, and cosmetics) usually have healthy babies. Some medications are necessary (e.g., for women with epilepsy, diabetes, and severe depression), but consultation should begin before conception.

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Many women assume that herbal medicines or over-the-counter drugs are safe. Not so: One expert explains, “Many over-the-counter drugs were grandfathered in with no studies of their possible effects during pregnancy” (quoted in Brody, 2013, p. D5).

Even doctors are not always careful. Opioids (narcotics) to reduce pain may harm the fetus, and aspirin may cause excessive bleeding during birth. Yet one study found that 23 percent of pregnant women on Medicaid receive a prescription for a narcotic (Desai et al., 2014).

Some doctors do not ask women if they are taking psychoactive drugs. For example, one Maryland study found that almost one-third of pregnant women were not asked if they drank (Cheng et al., 2011). Women over age 35 with college degrees were least likely to be queried. Did their doctors assume they knew the dangers? Wrong. Such women are more likely to drink during pregnancy than are younger women.

Women of all ages consult the Internet regarding medications in pregnancy. However, a study of 25 Web sites found that only 103 of the 235 medications listed as safe had been evaluated by TERIS (a respected national panel of teratologists). Further, of those 103, only 60 were considered safe. The rest were not proven harmful, but the experts said that more evidence was needed (Peters et al., 2013). Sometimes the same drug was on the safe list of one Internet site and the danger list of another.

A CASCADE OF RISK Even when evidence seems clear, the proper response is controversial. Pregnant women can be arrested and jailed for using alcohol or other psychoactive drugs in six states (Minnesota, North Dakota, Oklahoma, South Dakota, Tennessee, and Wisconsin).

Alicia Beltran, 14 weeks pregnant in Wisconsin, told her doctor that she had been addicted to pills but quit before she became pregnant, as confirmed by urine tests. The doctor ordered her to take anti-addiction medication. She thought that might harm her fetus and refused. She was arrested and taken in handcuffs to a holding cell (Eckholm, 2013).

Several women have been jailed when their newborns had illegal substances in their bloodstream (Eckholm, 2013). Such measures may do more harm than good if they make women avoid prenatal care or hospital births.

Every pregnancy and birth has multiple risks, so it is a mistake to blame any problem solely on the mother, or the doctor, or the community.

For instance, cerebral palsy (a disease marked by difficulties with movement) was once thought to be caused by birth procedures, such as forceps misused by the doctor. However, we now know that cerebral palsy results from genetic sensitivity, teratogens, and/or maternal infection (Mann et al., 2009), worsened by anoxia (insufficient oxygen) to the fetal brain at birth.

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Anoxia itself is part of a cascade. Normal birth involves moments of low oxygen, as evident from the fetal heart rate. How long anoxia can continue without harming the brain depends on genes, birthweight, gestational age, drugs in the bloodstream (either taken by the mother before birth or given during birth), and much else. Thus, anoxia is part of a cascade that may cause cerebral palsy. Likewise, almost every complication is the result of many factors.

Seeing a medical professional in the first trimester has many benefits: Women learn what to eat, what to do, and what to avoid. Some serious conditions, syphilis and HIV among them, can be diagnosed and treated before they harm the fetus. Prenatal tests (of blood, urine, and fetal heart rate as well as ultrasound) reassure parents, facilitating the crucial parent–child bond long before fetal movement is apparent.

In general, early care protects fetal growth, makes birth easier, and renders parents better able to cope. When complications appear (such as twins, gestational diabetes, and infections), early recognition increases the chance of a healthy birth.

Unfortunately, however, about 20 percent of early pregnancy tests raise anxiety instead of reducing it. It is now possible to use a simple blood test to indicate many chromosomal and genetic problems. The mother may learn information that she does not want to know (de Jong et al., 2015). Couples may argue about risks that they never discussed before.

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One specific example comes from a test in place for decades: alpha-fetoprotein (AFP). If it is too high or too low, it may indicate multiple fetuses, abnormal growth, or Down syndrome. Many such warnings are false positives; that is, they falsely suggest a problem that does not exist. Any warning, whether false or true, requires further testing, worry, and soul-searching. Consider the following.

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As you just read, small and immature newborns are more vulnerable to every teratogen and birth complication. The international cutoff for low birthweight (LBW)is 2,500 grams (5½ pounds). UNICEF estimated that 22 million low-birthweight babies were born in 2013.

Some LBW babies are very low birthweight (VLBW), under 1,500 grams (3 pounds, 5 ounces), and extremely low birthweight (ELBW), under 1,000 grams (2 pounds, 3 ounces). It is possible for a newborn to weigh as little as 500 grams. They are the most vulnerable: Half of them die even with excellent care, and none of them live without it (Lau et al., 2013).

Remember that fetal weight normally doubles in the last trimester of pregnancy, with most of that gain occurring in the final three weeks. Thus, a baby born preterm (three or more weeks early, no longer called premature) is usually, but not always, LBW.

In addition, some fetuses gain weight slowly throughout pregnancy and are small-for-dates, or small for gestational age (SGA). A full-term baby weighing only 2,600 grams and a 30-week-old fetus weighing only 1,000 grams are both SGA, even though the first is not technically LBW.

CAUSES OF LOW BIRTHWEIGHT Maternal or fetal illness might cause SGA or preterm birth, but maternal drug use is a more common cause. Every psychoactive drug slows fetal growth, with tobacco implicated in 25 percent of all LBW newborns worldwide.

Another common reason for slow growth and preterm birth is malnutrition. Women who begin pregnancy underweight, who eat poorly during pregnancy, or who gain less than 3 pounds (1.3 kilograms) per month in the last six months more often have underweight infants.

Unfortunately, many risk factors—underweight, undereating, underage, and smoking—tend to occur together. To make it worse, many such mothers live in poor neighborhoods, where pollution is high—another risk factor for low birthweight (Stieb et al., 2012).

The causes of low birthweight just mentioned rightly focus on the pregnant woman. However, fathers—and grandmothers, neighbors, and communities—are often crucial. Everyone who affects a pregnant woman also affects the fetus. She may be stressed because of her boss, her mother, her mother-in-law, and especially her partner. Because of the social system, it is not surprising that unintended pregnancies increase the incidence of low birthweight (Shah et al., 2011).

The role of the social network is most apparent in what is called the immigrant paradox. Many immigrants have difficulty getting education and well-paid jobs; their socioeconomic status is low. Low SES correlates with low birthweight.

Thus, immigrants should birth more LBW babies. But, paradoxically, their babies are generally healthier in every way, including in weight, than newborns of native-born women of the same gene pool (García Coll & Marks, 2012).

This was first called the Hispanic paradox because, although U.S. residents born in Mexico or South America average lower SES than people of Hispanic descent born in the United States, their newborns have fewer problems. The same paradox has been found for immigrants from the Caribbean, Africa, eastern Europe, and Asia. The crucial factor may be fathers and grandmothers, who keep pregnant immigrant women healthy and drug-free, counteracting the stress of poverty (Luecken et al., 2013).

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Newborns of Chinese descent born in the United States are an interesting case. If their mothers’ socioeconomic status is low, newborns weigh more and are less likely to die if their mothers were born in China, not in the United States. However, if the mother is college-educated, then the babies are healthier if their mothers are U.S.-born (Li & Keith, 2011).

This suggests that maternal education, household income, and social support all protect prenatal health. Of the three, social support may be most crucial, but the other two are important as well.

CONSEQUENCES OF LOW BIRTHWEIGHT You have already read that life itself is uncertain for the smallest newborns. Ranking worse than most developed nations—and just behind Cuba and Croatia—the infant mortality rate (death in the first year) of the United States is 34th in the world, about 6 deaths per 1,000 live births. One major reason is that the United States has more ELBW (under 1,000 grams) births (MacDorman et al., 2014).

For survivors born underweight, every developmental accomplishment—smiling, holding a bottle, walking, talking—is late. Low-birthweight babies experience cognitive difficulties as well as visual and hearing impairments. High-risk newborns become infants and children who cry more, pay attention less, disobey, and experience language delays (Aarnoudse-Moens et al., 2009; Stolt et al., 2014).

Longitudinal research from many nations finds that children who were at the extremes of SGA or preterm have many neurological problems in middle childhood, including smaller brain volume, lower IQs, and behavioral difficulties (Clark et al., 2013; Hutchinson et al., 2013; van Soelen et al., 2010). Even in adulthood, risks persist: Adults who were LBW are more likely to develop diabetes and heart disease.

Longitudinal data provide both hope and caution. Remember that risk analysis gives probabilities, not certainties—averages are not true in every case. By age 4, some ELBW infants are normal in brain and body development. Some adults were very small babies and have become happy and successful.

COMPARING NATIONS In some northern European nations, only 4 percent of newborns weigh under 2,500 grams; in several South Asian nations, including India, Pakistan, and the Philippines, more than 20 percent are that small. Worldwide, far fewer low-birthweight babies are born than two decades ago; as a result, neonatal deaths have been reduced by one-third (Rajaratnam et al., 2010).

Some nations, China and Chile among them, have improved markedly (Hellerstein et al., 2015). In many nations, community health programs emphasize prenatal health. That helps, according to a study provocatively titled Low birth weight outcomes: Why better in Cuba than Alabama? (Neggers & Crowe, 2013).

In some nations, notably in sub-Saharan Africa, the LBW rate is rising because global warming, HIV, food shortages, wars, and other problems affect pregnant women. Another nation with a troubling rate of LBW is the United States, where the rate fell throughout most of the twentieth century, reaching a low of 7.0 percent in 1990. But then it rose again, with the 2013 rate at 8.02 percent, ranging from under 6 percent in Alaska to over 12 percent in Mississippi (see Figure 2.8).

There are some encouraging data: The U.S. low-birthweight rate was even higher a few years ago, at 8.2 in 2007, and the rate of LBW newborns has fallen, while the medical care of babies born at less than 28 weeks is among the best in the world (MacDorman et al., 2014).

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WHAT HAVE YOU LEARNED?

Question 2.20

Most people born with trisomy-21, also called Down syndrome, have specific facial characteristics including a thick tongue, round face, and slanted eyes. Many also have hearing problems, heart abnormalities, muscle weakness, and short stature. They are usually slower to develop intellectually, especially in language, though their eventual intellect varies.

Question 2.21

The reason is evolutionary—carriers of certain recessive disorders were protected from deadly diseases. For example, sickle-cell carriers are unlikely to die from malaria, which was a major killer of those living in Africa.

Question 2.22

Some teratogens cause damage only during a critical period of development. For example, rubella can cause blindness and deafness if the exposure occurs during the embryonic period; if later (in the first or second trimester), exposure can cause brain damage.

Question 2.23

Genes can influence the effects of teratogens. For example, the Y chromosome makes male fetuses more vulnerable. They are more likely to be spontaneously aborted or stillborn and more likely to be harmed by teratogens than female fetuses are. Maternal genes may be important during pregnancy. One allele results in low levels of folic acid in a woman’s bloodstream. Her deficiency, via the placenta, affects the embryo, which may develop neural-tube defects.

Question 2.24

Early in pregnancy, an embryo exposed to heavy drinking can develop fetal alcohol syndrome (FAS), which distorts the facial features, especially the eyes, ears, and upper lip. Later in pregnancy, alcohol is a behavioral teratogen, the cause of fetal alcohol effects (FAE), leading to hyperactivity, poor concentration, impaired spatial reasoning, and slow learning.

Question 2.25

Prenatal care can help keep mother and baby healthy. Doctors can spot health problems early when they see mothers regularly. This allows doctors to treat them early. Doctors also can talk to pregnant women about things they can do to give their unborn babies a healthy start to life.

Question 2.26

Low birthweight (LBW) is defined as weight less than 2,500 grams (5 pounds, 8 ounces). This group is further grouped into two subgroups: very low birthweight (VLBW), which is less than 1,500 grams (3 pounds, 5 ounces); and extremely low birthweight (ELBW), which is less than 1,000 grams (2 pounds, 3 ounces).

Question 2.27

Being born preterm, maternal or fetal illness, maternal psychoactive drug use, and maternal malnutrition can all cause a baby to be LBW.

Question 2.28

Many LBW infants are late in milestones such as smiling, holding a bottle, walking, and talking. Cognitive difficulties as well as visual and hearing impairments may emerge as time passes. Even in adulthood, some risks persist—those born LBW have higher rates of obesity, heart disease, and diabetes.