Figure 3.6 Sensitive Periods in Prenatal Development
Source: Levine and Munsch (2010, p. 113).
More than 90% of pregnant women take prescription or over-the-counter (OTC) medications. The findings regarding the teratogenic effects of drugs are mixed, with some studies suggesting potential harm and others suggesting no ill effects of a given drug.
Gary Friedman/Los Angeles Times via Getty Images
Types of Teratogens
Prenatal development can be influenced by many contextual factors, including maternal consumption of over-the-counter (OTC), prescription, and recreational drugs; illness; environmental factors; and more. Sometimes a pregnant woman and her doctor must make a difficult choice between forgoing a needed prescription drug and putting the fetus at risk. In those cases, the woman and her doctor must weigh not just the benefits of the medication but also the potential harm from forgoing it compared with the risks to the fetus. Frequently, the risks are deemed as justified to protect the woman’s mental and physical health. And, in any case, a woman may not know she is pregnant until after the first few weeks of the embryonic stage are already past. Thus, in the real world, almost no pregnancy can be entirely free of exposure to teratogens. However, each year, about 97% of infants are born without defects (Centers for Disease Control and Prevention, 2017a).
Prescription and Nonprescription Drugs
More than 90% of pregnant women take prescription or OTC medications (Servey & Chang, 2014). Prescription drugs that can act as teratogens include antibiotics, certain hormones, antidepressants, anticonvulsants, and some acne drugs (Webster et al., 2018). In several cases, physicians have unwittingly prescribed drugs to ease pregnant women’s discomfort that caused harm to the fetus. For example, in the late 1950s and early 1960s, many pregnant women were prescribed thalidomide to prevent morning sickness. However, it was found that taking thalidomide 4 to 6 weeks after conception (in some cases, even just one dose) caused deformities of the child’s arms and legs, and, less frequently, damage to the ears, heart, kidneys, and genitals (Fraga et al., 2016). Isotretinoin, a form of vitamin A used to treat acne, is a potent teratogen associated with miscarriage as well as severe face, heart, and central nervous system abnormalities, as well as intellectual disability (Henry et al., 2016; Wilson, 2016). The teratogenic effect of isotretinoin is so severe that the U.S. Food and Drug Administration (2010) requires that women prescribed isotretinoin take physician-administered pregnancy tests for 2 months prior to beginning treatment and agree to use two methods of birth control and complete a monthly pregnancy test each month while taking it.
Nonprescription drugs, such as diet pills and cold medicine, can also cause harm, but research on OTC drugs lags far behind research on prescription drugs, and we know little about the teratogenic effect of many OTC drugs (Hussain & Ashmead, 2017). Frequently, findings regarding the teratogenic effects of drugs are mixed, with some studies suggesting potential harm and others suggesting no ill effects of a given drug. For example, some research suggests that high doses of the common painkiller aspirin may be associated with an increased risk of miscarriage and poor fetal growth (Elkarmi, Abu-Samak, & Al-Qaisi, 2007; Li, Liu, & Odouli, 2003). Yet low doses of aspirin may have benefits. Physicians commonly prescribe a low dose to prevent and treat preeclampsia and high blood pressure during pregnancy (Roberge, Bujold, & Nicolaides, 2017). Likewise, the most common OTC drug consumed during pregnancy, caffeine, found in coffee, tea, cola drinks, and chocolate, appears to be safe in low doses (200 milligrams or about one cup per day; March of Dimes, 2015). Heavy caffeine consumption, however, is associated with an increased risk for miscarriage and low birthweight (Chen et al., 2014, 2016).
Fetal alcohol syndrome is associated with distinct facial characteristics, growth deficiencies, and deficits in intellectual development, language, motor coordination, and the combined abilities to plan, focus attention, and problem solve that persist throughout childhood and into adulthood.
Susan Astley, PhD, University of Washington
Alcohol
An estimated 10% to 20% of Canadian and U.S. women report consuming alcohol during pregnancy (Alshaarawy, Breslau, & Anthony, 2016; Popova, Lange, Probst, Parunashvili, & Rehm, 2017).
Indeed, alcohol abuse during pregnancy has been identified as the leading cause of developmental disabilities (Webster et al., 2018). Fetal alcohol spectrum disorders refer to the continuum of effects of exposure to alcohol, which vary with the timing and amount of exposure (Hoyme et al., 2016). Fetal alcohol spectrum disorders are estimated to affect as many as 2% to 5% of younger schoolchildren in the United States and Western Europe (May et al., 2014). At the extreme end of the spectrum is fetal alcohol syndrome (FAS), a cluster of defects appearing after heavy prenatal exposure to alcohol. FAS is associated with a distinct pattern of facial characteristics (such as small head circumference, short nose, small eye opening, and small midface), pre- and postnatal growth deficiencies, and deficits in intellectual development, school achievement, memory, visuospatial skills, attention, language, problem solving, motor coordination, and the combined abilities to plan, focus attention, problem solve, and use goal-directed behavior (Gupta, Gupta, & Shirasaka, 2016; Wilhoit, Scott, & Simecka, 2017). The effects of exposure to alcohol within the womb persist throughout childhood and adolescence and are associated with cognitive, learning, and behavioral problems from childhood and adolescence through adulthood (Mamluk et al., 2016; Panczakiewicz et al., 2016; Rangmar et al., 2015).
Even moderate drinking is harmful as children may be born displaying some but not all of the problems of FAS, fetal alcohol effects (Hoyme et al., 2016). Consuming 7 to 14 drinks per week during pregnancy is associated with lower birth size, growth deficits through adolescence, and deficits in attention, memory, and cognitive development (Alati et al., 2013; Flak et al., 2014; Lundsberg et al., 2015). Even less than one drink per day has been associated with poor fetal growth and preterm delivery (Mamluk et al., 2017). Scientists have yet to determine if there is a safe level of drinking, but the only way to be certain of avoiding alcohol-related risks is to avoid alcohol during pregnancy altogether.
Cigarette Smoking
Every package of cigarettes sold in the United States includes a warning about the dangers of smoking while pregnant. Fetal deaths, premature births, and low birthweight are up to twice as frequent in mothers who are smokers than in those who do not smoke (Juárez & Merlo, 2013). Infants exposed to smoke while in the womb are prone to congenital heart defects, respiratory problems, and sudden infant death syndrome and, as children, show more behavior problems, have attention difficulties, and score lower on intelligence and achievement tests (He et al., 2017; Lee & Lupo, 2013; Sutin et al., 2017). Moreover, maternal smoking during pregnancy shows epigenetic effects on offspring,