Infants and Children in Context. Tara L. Kuther

and opioids (Gupta, 2017; Neradugomma et al., 2018; Serra et al., 2017).

      About 22 days after conception marks a particularly important change. The endoderm folds to form the neural tube, which will develop into the central nervous system (brain and spinal cord) (Webster et al., 2018). Now the head can be distinguished. A blood vessel that will become the heart begins to pulse and blood begins to circulate throughout the body. During days 26 and 27, arm buds appear, followed by leg buds on days 28 through 30. At about this time, a tail-like appendage extends from the spine, disappearing at about 55 days after conception (Sadler, 2018). The brain develops rapidly and the head grows faster than the other parts of the body during the fifth week of development. The eyes, ears, nose, and mouth begin to form during the sixth week. Upper arms, forearms, palms, legs, and feet appear. The embryo shows reflex responses to touch.

      During the seventh week, webbed fingers and toes are apparent; they separate completely by the end of the eighth week. A ridge called the indifferent gonad appears; it will develop into the male or female genitals, depending on the fetus’s sex chromosomes (Moore & Persaud, 2016). The Y chromosome of the male embryo instructs it to secrete testosterone, causing the indifferent gonad to create testes. In female embryos, no testosterone is released, and the indifferent gonad produces ovaries. The sex organs take several weeks to develop. The external genital organs are not apparent until about 12 weeks.

      At the end of the embryonic period, 8 weeks after conception, the embryo weighs about one-seventh of an ounce and is 1 inch long. All of the basic organs and body parts have formed in a very rudimentary way. The embryo displays spontaneous reflexive movements, but it is still too small for the movements to be felt by the mother (Hepper, 2015). Serious defects that emerge during the embryonic period often cause a miscarriage, or spontaneous abortion (loss of the fetus); indeed, most miscarriages are the result of chromosomal abnormalities. The most severely defective organisms do not survive beyond the first trimester, or third month of pregnancy. It is estimated that up to 45% of all conceptions abort spontaneously, and most occur before the pregnancy is detected (Bienstock, Fox, & Wallach, 2015).

      Description

      Figure 3.2 Germinal Period

      Source: Levine and Munsch (2010, p. 102).

      Fetal Period (9 Weeks to Birth)

      During the fetal period, from the ninth week to birth, the organism, called a fetus, grows rapidly, and its organs become more complex and begin to function. Now all parts of the fetus’s body can move spontaneously, the legs kick, and the fetus can suck its thumb (an involuntary reflex). By the end of the 12th week, the upper limbs have almost reached their final relative lengths, but the lower limbs are slightly shorter than their final relative lengths (Sadler, 2018).

      By the 14th week, limb movements are coordinated, but they will be too slight to be felt by the mother until about 17 to 20 weeks. The heartbeat gets stronger. Eyelids, eyebrows, fingernails, toenails, and tooth buds form. The first hair to appear is lanugo, a fine down-like hair that covers the fetus’s body; it is gradually replaced by human hair. The skin is covered with a greasy material called the vernix caseosa, which protects the fetal skin from abrasions, chapping, and hardening that can occur with exposure to amniotic fluid (Moore & Persaud, 2016). At 21 weeks, rapid eye movements begin, signifying an important time of growth and development for the fetal brain. The brain begins to become more responsive. For example, startle responses have been reported at 22 to 23 weeks in response to sudden vibrations and noises (Hepper, 2015). During weeks 21 to 25, the fetus gains substantial weight, and its body proportions become more like those of a newborn infant. Growth of the fetal body begins to catch up to the head, yet the head remains disproportionately larger than the body at birth.

      During the last 3 months of pregnancy, the fetal body grows substantially in weight and length; specifically, it typically gains over 5 pounds and grows 7 inches. At about 28 weeks after conception, brain development grows in leaps and bounds. The cerebral cortex develops convolutions and furrows, taking on the brain’s characteristic wrinkly appearance (Andescavage et al., 2016). The fetal brain wave pattern shifts to include occasional bursts of activity, similar to the sleep-wake cycles of newborns. By 30 weeks, the pupils of the eyes dilate in response to light. At 35 weeks, the fetus has a firm hand grasp and spontaneously orients itself toward light.

      Although the expected date of delivery is 266 days or 38 weeks from conception (40 weeks from the mother’s last menstrual period), about 1 in every 10 American births is premature (Centers for Disease Control and Prevention, 2017e). The age of viability—the age at which advanced medical care permits a preterm newborn to survive outside the womb—begins at about 22 weeks after conception (Sadler, 2018). Infants born before 22 weeks rarely survive more than a few days, because their brain and lungs have not begun to function. Although a 23-week fetus born prematurely may survive in intensive care, its immature respiratory system places it at risk; only about one-third of infants born at 23 weeks’ gestation survive (Stoll et al., 2015). At about 26 weeks, the lungs become capable of breathing air and the premature infant stands a better chance of surviving if given intensive care. About 80% of infants born at 25 weeks survive, and 94% of those born at 27 weeks also survive. Premature birth has a variety of causes, including many environmental factors.

      Our discussion thus far has emphasized fetal development; however, expectant mothers also experience radical physical changes during pregnancy. In addition to changes in body weight and shape, pregnancy is accompanied by changes in brain structure and function, as discussed in the Lives in Context feature.

      Lives in Context: Biological Influences

      Pregnancy and the Maternal Brain

      The developing embryo and fetus receive a great deal of research attention, but what does pregnancy mean for mothers’ development? Women’s bodies undergo a radical transformation during pregnancy. For example, the hormone progesterone increases up to 15-fold and is accompanied by a flood of estrogen that is greater than the lifelong exposure prior to pregnancy. Hormonal shifts are associated with brain changes during puberty as well as later in life. Do the hormonal changes with pregnancy influence women’s brain structure? Animal research suggests that pregnancy is accompanied by neurological changes, including changes in neural receptors, neuron generation, and gene expression, that are long-lasting (Kinsley & Amory-Meyer, 2011). It is likely that pregnancy is also associated with neural changes in humans, but there is little research to date (Hillerer, Jacobs, Fischer, & Aigner, 2014).

      In a recent groundbreaking study, Elseine Hoekzema and colleagues (2017) conducted brain scans of women who were attempting to become pregnant for the first time as well as their partners. Women who became pregnant were scanned again after giving birth and at least 2 years later. The fathers and women who had not become pregnant were also assessed. The new mothers experienced reductions in the brain’s gray matter, signifying increased neural efficiency in regions of the brain involved in social cognition, specifically, the ability to sense another person’s emotions and perspective. This corresponds with prior findings suggesting that pregnancy is associated with the enhanced ability to recognize faces, especially those displaying emotions (Pearson, Lightman, & Evans, 2009). Gestational alterations in the brain structures that are implicated in social processes may offer an adaptive advantage to mothers by facilitating their ability to recognize the needs of their children and to promote mother–infant bonding (Hoekzema et al., 2017). The changes in gray matter volume predicted mothers’ attachment to their infants in the postpartum period, as indicated by mothers’ increased neural activity in response to viewing photos of their infant compared with other infants. The pregnancy-related neurological changes were so marked and predictable that all of the women could be classified as having undergone pregnancy or not on the basis of the volume changes in gray matter. Notably, fathers did not show a change in gray matter volume, suggesting that the neural effects of pregnancy are biological in nature rather than associated with the contextual changes that