Problems and Solutions

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.

Abnormal Genes and Chromosomes

Video: Genetic Disorders

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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Question 2.19

OBSERVATION QUIZ

How many characteristics can you see that indicate that Daniel has Down syndrome?

Individuals with Down syndrome vary in many traits, but visible here are five common ones. Compared to most children his age, including his classmate beside him, Daniel has a rounder face, narrower eyes, shorter stature, larger teeth and tongue, and—best of all—a happier temperament.

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Universal Happiness All young children delight in painting brightly colored pictures on a big canvas, but this scene is unusual for two reasons: Daniel has trisomy-21, and this photograph was taken at the only school in Chile where normal and special-needs children share classrooms.

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).

Down syndrome

A condition in which a person has 47 chromosomes instead of the usual 46, with three rather than two chromosomes at the 21st position. People with Down syndrome typically have distinctive characteristics, including unusual facial features (thick tongue, round face, slanted eyes), heart abnormalities, and language difficulties. (Also called trisomy-21.)

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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She Laughs Too Much No, not the smiling sister, but the 10-year-old on the right, who has Angelman syndrome. She inherited it from her mother’s chromosome 15. Fortunately, her two siblings inherited the mother’s other chromosome 15 and are normal. If she had inherited the identical deletion on her father’s chromosome 15, she would have developed Prader-Willi syndrome, which would cause her to be overweight as well as always hungry and often angry. With Angelman syndrome, however, laughing, even at someone’s pain, is a symptom.

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).

fragile X syndrome

A genetic condition that involves the X chromosome and that causes slow development.

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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Harm to the Fetus

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).

teratogen

Any agent or condition, including viruses, drugs, and chemicals, that can impair prenatal development, resulting in birth defects or complications.

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.

behavioral teratogens

Agents and conditions that can harm the prenatal brain, impairing the future child’s intellectual and emotional functioning.

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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Swing High and Low Adopted by loving parents but born with fetal alcohol syndrome, Philip, shown here at age 11, sometimes threatened to kill his family members. His parents sent him to this residential ranch in Eureka, Montana (non-profit, tuition $3,500 a month) for children like him. This moment during recess is a happy one; it is not known whether he learned to control his fury.

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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).

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Figure 2.7: FIGURE 2.7 One More Reason to Plan a Pregnancy The embryonic period, before a woman knows she is pregnant, is the most sensitive time for causing structural birth defects. However, at no time during pregnancy is the fetus completely safe from harm. Individual differences in susceptibility to teratogens may be caused by a fetus’s genetic makeup or peculiarities of the mother, including the effectiveness of her placenta or her overall health. The dose and timing of the exposure are also important.

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).

threshold effect

A situation in which a certain teratogen is relatively harmless in small doses but becomes harmful once exposure reaches a certain level (the threshold).

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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Table 2.5: Table 2.4 Before Pregnancy

What Prospective Mothers Should Do

  1. Plan the pregnancy.

  2. Take a daily multivitamin with folic acid.

  3. Avoid binge drinking (defined as four or more drinks in a row).

  4. Update immunizations against all teratogenic viruses, especially rubella.

  5. Gain or lose weight, as appropriate.

  6. Reassess use of prescription drugs.

  7. Develop daily exercise habits.

What Prospective Mothers Really Do (U.S. Data)

  1. At least one-fourth of all pregnancies are not intended.

  2. About 60 percent of women aged 18 to 45 do not take multivitamins.

  3. One in seven women in their childbearing years binge drink.

  4. Unlike in many developing nations, relatively few pregnant women in the United States lack basic immunizations.

  5. About one-fourth of all U.S. women of childbearing age are obese, and about 5 percent are underweight. Both extremes increase complications.

  6. Ninety percent of pregnant women take prescription drugs (not counting vitamins).

  7. More than half of women of childbearing age do not exercise regularly.

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.

fetal alcohol syndrome (FAS)

A cluster of birth defects, including abnormal facial characteristics, slow physical growth, and intellectual disabilities, that may occur in the child of a woman who drinks alcohol while pregnant.

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.

LaunchPad

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Video Activity: Teratogens explores the factors that enable or prevent teratogens from harming a developing fetus.

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.

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Smoke-Free Babies Posters such as this one have had an impact. Smoking among adults is only half of what it was 30 years ago. One-third of women smokers quit when they know they are pregnant, while the other two-thirds cut their smoking in half. Unfortunately, the heaviest smokers are least likely to quit—they need more than posters to motivate them to break the habit.

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.

cerebral palsy

A disorder that results from damage to the brain’s motor centers. People with cerebral palsy have difficulty with muscle control, so their speech and/or body movements are impaired.

anoxia

A lack of oxygen that, if prolonged, can cause brain damage or death.

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.

A VIEW FROM SCIENCE

Conflicting Advice

Pregnant women want to know about the thousands of drugs, chemicals, and diseases that cause fetal harm. However, the scientific method is designed to be cautious. It takes years for longitudinal research, testing of alternative hypotheses, and replication before solid conclusions are reached. Only after this process did all scientists agree on such (now obvious) teratogens as rubella and cigarettes.

One current dispute is whether pesticides should be allowed on the large farms that produce most of the fruits and vegetables for consumption in the United States. No biologist doubts that pesticides harm frogs, fish, and bees, but the pesticide industry insists that careful use (e.g., spraying on plants, not workers) does not harm people.

Developmentalists, however, worry that pregnant women who breathe these toxins might have children with brain damage. As one scientist said, “Pesticides were designed to be neurotoxic . . . Why should we be surprised if they cause neurotoxicity?” (Lanbhear, quoted in Mascarelli, 2013, p. 741).

For example, umbilical cord blood proves that many fetuses are exposed to chlorpyrifos, a pesticide. Longitudinal research finds that these children have lower intelligence and more behavior problems than other children (Horton et al., 2012).

However, Dow Chemical Company, which sells the pesticide, argues that the research does not take into account confounding factors, such as the living conditions of farmworkers’ children (Mascarelli, 2013). If a child who lives in a shack and attends a different school every few months has learning disabilities, does it matter whether his mother worked in the fields with pesticides when she was pregnant?

The U.S. government has banned chlorpyrifos from household use (it once was commonly used to kill roaches and ants), but it is still used in agriculture and in homes in other nations. In this dispute, developmentalists choose to protect the fetal brain, which is why this chapter advises pregnant women to avoid pesticides. Is that overly cautious?

On many other possible teratogens, developmentalists themselves are conflicted. Fish consumption is an example.

Pregnant women in the United States are told to eat less fish, but those in the United Kingdom are told to eat more fish. The reason for these opposite messages is that fish contains mercury (a teratogen) and DHA (an omega-3 fatty acid needed for fetal brain development). Scientists weigh the benefits and risks, wondering how to teach women to judge each kind of fish and where it swam, choosing benefits while avoiding risks (Lando & Lo, 2014).

To make all this more difficult, pregnant women are, ideally, happy and calm: Stress and anxiety affect the fetus. Pregnancy often increases fear and anxiety (Rubertsson et al., 2014); scientists do not want to add to the worry. Prospective parents want clear, immediate answers, yet scientists cannot always provide them.

Prenatal Testing

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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false positives

The result of a laboratory test (blood, urine or sonogram) that suggests an abnormality that is not present.

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.

A CASE TO STUDY

False Positives and False Negatives

John and Martha, both under age 35, were expecting their second child. Martha’s initial prenatal screening revealed low alpha-fetoprotein, which could indicate Down syndrome.

Another blood test was scheduled. . . .

John asked, “What exactly is the problem?” . . .

“We’ve got a one in eight hundred and ninety-five shot at a retarded baby.”

John smiled, “I can live with those odds.”

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Happy Boy Martha Beck not only loves her son Adam (shown here), but she also writes about the special experiences he has brought into the whole family’s life—hers, John’s, and their other children’s. She is “pro-choice”; he is a chosen child.

“I’m still a little scared.”

He reached across the table for my hand. “Sure,” he said, “that’s understandable. But even if there is a problem, we’ve caught it in time. . . . The worst-case scenario is that you might have to have an abortion, and that’s a long shot. Everything’s going to be fine.” . . .

“I might have to have an abortion?” The chill inside me was gone. Instead I could feel my face flushing hot with anger. “Since when do you decide what I have to do with my body?”

John looked surprised. “I never said I was going to decide anything,” he protested. “It’s just that if the tests show something wrong with the baby, of course we’ll abort. We’ve talked about this.”

“What we’ve talked about,” I told John in a low, dangerous voice, “is that I am pro-choice. That means I decide whether or not I’d abort a baby with a birth defect. . . . I’m not so sure of this.”

“You used to be,” said John.

“I know I used to be.” I rubbed my eyes. I felt terribly confused. “But now . . . look, John, it’s not as though we’re deciding whether or not to have a baby. We’re deciding what kind of baby we’re willing to accept. If it’s perfect in every way, we keep it. If it doesn’t fit the right specifications, whoosh! Out it goes.”. . .

John was looking more and more confused. “Martha, why are you on this soapbox? What’s your point?”

“My point is,” I said, “that I’m trying to get you to tell me what you think constitutes a ‘defective’ baby. What about . . . oh, I don’t know, a hyperactive baby? Or an ugly one?”

“They can’t test for those things and—

“Well, what if they could?” I said. “Medicine can do all kinds of magical tricks these days. Pretty soon we’re going to be aborting babies because they have the gene for alcoholism, or homosexuality, or manic depression. . . . Did you know that in China they abort a lot of fetuses just because they’re female?” I growled. “Is being a girl ‘defective’ enough for you?”

“Look,” he said, “I know I can’t always see things from your perspective. And I’m sorry about that. But the way I see it, if a baby is going to be deformed or something, abortion is a way to keep everyone from suffering—especially the baby. It’s like shooting a horse that’s broken its leg. . . . A lame horse dies slowly, you know? . . . It dies in terrible pain. And it can’t run anymore. So it can’t enjoy life even if it doesn’t die. Horses live to run; that’s what they do. If a baby is born not being able to do what other people do, I think it’s better not to prolong its suffering.”

“. . . And what is it,” I said softly, more to myself than to John, “what is it that people do? What do we live to do, the way a horse lives to run?”

[Beck, 2011, pp. 134–136, 138]

The second AFP test was in the normal range, “meaning that there was no reason to fear . . . Down syndrome” (p. 142). John and Martha no longer discussed abortion.

The opposite of a false positive is a false negative, a mistaken assurance that all is well. Amniocentesis revealed that the second AFP was a false negative. Their fetus had Down syndrome after all. John and Martha had another angry discussion, and Martha decided to give birth to Adam, who has Down syndrome. Years later they had a third child. When Adam was in early adolescence, Martha and John divorced.

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Low Birthweight

low birthweight (LBW)

A body weight at birth of less than 5½ pounds (2,500 grams).

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.

very low birthweight (VLBW)

A body weight at birth of less than 3 pounds, 5 ounces (1,500 grams).

extremely low birthweight (ELBW)

A body weight at birth of less than 2 pounds, 3 ounces (1,000 grams).

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).

preterm birth

A birth that occurs three or more weeks before the full 38 weeks of the typical pregnancy have elapsed—that is, at 35 or fewer weeks after conception.

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.

small for gestational age (SGA)

Having a body weight at birth that is significantly lower than expected, given the time since conception. For example, a 5-pound (2,265-gram) newborn is considered SGA if born on time but not SGA if born two months early. (Also called small-for-dates.)

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).

Watch Video: Low Birthweight in India, which discusses the causes of LBW among babies in India.

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).

immigrant paradox

The surprising fact that immigrants tend to be healthier than U.S. born residents of the same ethnicity. This was first evident among immigrant births to Mexican Americans. Such births are less often low birth weight than the non-immigrant average.

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).

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Figure 2.8: FIGURE 2.8 Getting Better Some public health experts consider the rate of low birthweight to indicate of national health, since both reflect the same causes. If that is true, the world is getting healthier, since the LBW world average was 28 percent in 2009 but 16 percent in 2012. When all nations are included, 47 report LBW at 6 per 100 or lower (United States and United Kingdom are not among them).

THINK CRITICALLY: Food scarcity, drug use, and unmarried parenthood have all been suggested as reasons for the LBW rate in the United States. Which is it—or are there other factors?

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

1. What are the consequences if an infant is born with trisomy-21?

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

2. Why are some recessive traits (such as sickle-cell) quite common?

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

3. How does the timing of exposure to a teratogen affect the risk of harm to the fetus?

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

4. How do genes increase or decrease risk to a fetus?

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

5. What are the potential consequences of drinking alcohol during pregnancy?

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

6. What are the benefits of prenatal care?

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

7. What are the differences among LBW, VLBW, and ELBW?

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

8. What would cause a newborn to be LBW?

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

9. What are the consequences of low birthweight in childhood and adulthood?

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.