Pregnancy is not only a period of development for the embryo, but for the mother as well. Brain plasticity during pregnancy and the postpartum period is adaptive, as it helps women adapt to motherhood and the challenges of caring for a newborn. Moreover, research suggests that increased plasticity continues well after birth. One study of brain images of women 1 to 2 days after childbirth and 4–6 weeks later found a rejuvenation effect whereby women’s brains showed enhanced plasticity, appearing on average about 5 years younger in the weeks after birth (Luders et al., 2018). However, some scientists argue that enhanced plasticity can promote development but it may also increase women’s sensitivity to stress and vulnerability to mental disorders, such as depression (Barba-Müller, Craddock, Carmona, & Hoekzema, 2019), underlining the importance of support for new mothers.
What Do You Think?
1 From an evolutionary developmental perspective (see Chapter 1), why might these pregnancy-related brain changes occur?
2 How can mothers take advantage of the plasticity that accompanies pregnancy and the postpartum period?
3 What are some ways to support women during the transition to motherhood? ●
Thinking in Context 3.1
1 “The most critical time in prenatal development is the end because the fetus is most like a baby,” explains Rita. To what extent do you agree with Rita? What do we know about the process of prenatal development?
2 What might be some of the implications of the timing of prenatal development for the behavior of pregnant women and those who are considering becoming pregnant?
Environmental Influences on Prenatal Development
Prenatal development unfolds along a programmed path, a predictable pattern of change. However, environmental factors can interfere with the processes of prenatal development. A teratogen is an agent, such as a disease, drug, or other environmental factor, that disrupts prenatal development, increasing the risk of abnormalities, defects, and even death. The field of teratology attempts to find the causes of birth defects so that they may be avoided. Health care providers help pregnant women and those who intend to become pregnant to be aware of teratogens and avoid them, as much as possible, to maximize the likelihood of having a healthy baby.
Principles of Teratology
Different teratogens affect development in different ways. Moreover, it is not always easy to predict the harm caused by teratogens. Generally, several principles can account for the varied effects of exposure to teratogens on prenatal development (Moore & Persaud, 2016; Sadler, 2015).
Critical Periods. The extent to which exposure to a teratogen disrupts prenatal development depends on the stage of prenatal development when exposure occurs. That is, there are critical periods during prenatal development in which the developing organism is more susceptible to damage from exposure to teratogens. Exposure to teratogens during the germinal stage can interfere with cell division and prevent implantation; however, during this stage most women are unaware that they are pregnant and the effects of teratogens often go unnoticed. It is during the embryonic period that the embryo is most sensitive to the harmful effects of teratogens (Webster et al., 2018). Structural defects occur when the embryo is exposed to a teratogen while that part of the body is developing. As shown in Figure 3.3, each organ of the body has a sensitive period in development during which it is most susceptible to damage from teratogens such as drugs, alcohol, and environmental contaminants. Once a body part is fully formed, it is less likely to be harmed by exposure to teratogens; however, some body parts, like the brain, remain vulnerable throughout pregnancy.DescriptionFigure 3.3 Sensitive Periods in Prenatal DevelopmentSource: Levine and Munsch (2010, p. 113).
Dose. The amount of exposure (i.e., dose level) to a teratogen influences its effects. Generally, the greater the dose and the longer the period of exposure, the more damage to development. However, teratogens also differ in their strength. Some teratogens, like alcohol, display a powerful dose–response relationship so that larger doses, or heavier and more frequent drinking, result in greater damage (Muggli et al., 2017).
Individual Differences. Individuals vary in their susceptibility to particular teratogens based on the genetic makeup of both the organism and mother, as well as the quality of the prenatal environment. How an organism responds to a teratogen may vary with its genetic vulnerability. That is, teratogens increase the risk of defects for all organisms, but responses may vary such that some organisms show severe defects, others show more mild defects, and some may display normal development. The mother’s genetic makeup and the prenatal environment (e.g., nutrition) may also increase or decrease the likelihood of teratogenic defects.
Complicated Effects. Different teratogens can cause the same birth defect, and a variety of birth defects can result from the same teratogen. Also, some teratogenic effects may not be noticeable at birth but instead emerge later in life. Sleeper effects refer to detrimental outcomes of exposure to teratogens and early risks that appear only later in development. For example, infants born to women who consumed diethylstilbestrol (DES), a hormone that was widely prescribed between 1945 and 1970 to prevent miscarriages, were born healthy but as adults were more likely to experience problems with their reproductive systems. Daughters born to mothers who took DES were more likely to develop a rare form of cervical cancer, have miscarriages, and give birth to infants who were premature or low birthweight (Conlon, 2017).
Types of Teratogens
Prenatal development can be influenced by many contextual factors, including environmental factors, maternal illness, and maternal consumption of over-the-counter (OTC), prescription, and recreational drugs, among others. 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 risks to the fetus but the benefits of the medication to the mother and the potential harm from forgoing it. Frequently, the risks are deemed as justified to protect the woman’s mental and physical health. In most cases, women are unaware of their pregnancies until after the first few weeks of the embryonic stage. 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). Next, we examine common teratogens.
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,