Читать книгу Lifespan Development - Tara L. Kuther - Страница 155

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.

During the third trimester, pregnant women and their caregivers are mindful that the baby may be born prematurely. 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, 2017b). 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, 2015). 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.