The first two weeks of prenatal growth are called the germinal period. During this time, the single-
The third through eighth weeks after conception make up the embryonic period. The heart begins to beat, and the eyes, ears, nose, and mouth form, the skeletal outline and inner organs form. By the eighth week, the embryo has the basic organs and features of a human, with the exception of the sex organs.
The fetal period extends from the ninth week until birth. In the ninth week, the sexual organs develop. By the end of the third month, all the organs and body structures have formed. The fetus attains viability at 22 weeks, when the brain can regulate basic body functions.
The average fetus gains approximately 4½ pounds (2,040 grams) from the 6th to the 9th month, weighing 7½ pounds (3,400 grams) at birth. Maturation of brain, lungs, and heart ensures survival of more than 99 percent of all full-
Birth typically begins with contractions that push the fetus out of the uterus and then through the vagina. The Apgar scale, which rates the newborn at one minute and again at five minutes after birth, provides a quick evaluation of the infant’s health.
Medical assistance can speed contractions, dull pain, and save lives. However, many aspects of medicalized birth have been criticized as impersonal and unnecessary, including about half the cesareans performed in the United States. Contemporary birthing practices—
Risk analysis is crucial in predicting prenatal development, because no teratogen always causes harm, but many factors affect whether harm will occur and how serious it will be.
Some teratogens (diseases, drugs, and pollutants) cause physical impairment, especially during the first weeks of development. Others, called behavioral teratogens, harm the fetal brain and therefore, in later life, impair cognitive abilities and affect personality.
Whether a teratogen harms an embryo or fetus depends on timing, dose, and genes. Public and personal health practices can protect against prenatal complications. Support and help from the father and other family members affect the pregnant woman’s health.
Birth complications, such as unusually long and stressful labor that includes anoxia (a lack of oxygen to the fetus), have many causes, and are made worse by teratogens and other prenatal factors.
Low birthweight (under 5½ pounds, or 2,500 grams), very low birthweight (VLBW—
Compared with full-
National differences are apparent in the frequency of low birth weight, primarily because of undernourished mothers. In addition, family support may be crucial, and may be one reason for the immigration paradox, that in developed nations, women born in other nations are more likely to have full term newborns than native-
Humans are social animals, from the moment of birth. The Brazelton Neonatal Behavioral Assessment Scale measures 46 newborn behaviors, 20 of which are reflexes. In many ways newborns contribute to early family bonding.
Fathers can be supportive during pregnancy as well as helpful in birth. Paternal support correlates with shorter labor and fewer complications. Some fathers become so involved with the pregnancy and birth that they experience couvade.
Many women feel unhappy, incompetent, or unwell after giving birth. This may reach the level of postpartum depression. Fathers may have a crucial influence on the health and welfare of mother and child. Ideally, a parental alliance forms to help the child develop well.
Kangaroo care benefits all babies but especially those who are vulnerable. Mother–
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