Читать книгу Lifespan Development - Tara L. Kuther - Страница 154

By the 14th week, at the start of the second trimester, 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 (K. L. 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.