Within hours after conception, the zygote begins duplication and division. After about the 16-cell stage, duplication and division continue and a third process, differentiation, begins. Soon cells specialize, taking different forms and reproducing at various rates, depending on where they are located.
The brain and spinal column, eyes, ears, nose, and mouth start to form, as do the heart, arms, and legs. This is followed by the upper arm, forearm, palms, webbed fingers, legs, knees, feet, and webbed toes.
The critical difference between life and death, or between a fragile preterm baby and a robust newborn, is maturation of the neurological, respiratory, and cardiovascular systems. In the last three months of prenatal life, the lungs begin to expand and contract, exercising muscles involved in breathing by using the amniotic fluid as a substitute for air. The valves of the heart go through a final maturation, as do the arteries and veins throughout the body. Among other things, this helps to prevent “brain bleeds,” one of the hazards of preterm birth in which paper-thin blood vessels in the skull collapse.
Cesareans make scheduling a baby’s delivery easier than the unpredictable vaginal birth, and the actual delivery is quicker than a vaginal birth. Cesareans also carry an added bonus for the hospital since they are quite expensive.
C-sections are warranted in only about 15 percent of births. While they are generally safe, they are often performed for convenience’s sake. However, they result in more complications after birth and reduce breast-feeding. By age 3, children born by cesarean have double the rate of childhood obesity compared to those born vaginally.
Doctors have sophisticated medical training and may have specialized in the delivery of babies. Midwives have training in the birth process and are often as skilled as physicians in delivery. Doulas support laboring women throughout labor, delivery, and the start of breast-feeding.
Teratogens that affect the developing body structure include medicinal drugs, psychoactive drugs, and social and behavioral factors. Teratogens that affect the brain of the developing person include exposure to diseases (such as rubella, toxoplasmosis, and infections), pollutants (such as lead, mercury, PCBs, and cleaning compounds), and radiation.
Some teratogens cause damage only during a critical period of development. For example, rubella can cause blindness and deafness if the exposure occurs during the embryonic period; if later in the first or in the second trimester, exposure can cause brain damage.
Some teratogens cause damage only during a critical period when a particular part of the body is forming. Because the early days are critical, most obstetricians today recommend that before pregnancy women need to avoid drugs (including alcohol), supplement a balanced diet with extra folic acid, iron, and other crucial vitamins, and update their immunizations. Other factors—such as genetic vulnerability or protection, and dose of the teratogen—can play a role in whether a particular teratogen will have a negative effect.
One maternal allele results in low levels of folic acid during pregnancy, and that can produce neural-tube defects such as spina bifida, in which the tail of the spine is not enclosed properly. Neural-tube defects are more common in certain ethnic groups (Irish, English, and Egyptian) than in others. Folic acid supplements before and during pregnancy are strongly recommended.
Early in pregnancy, an embryo exposed to heavy drinking can develop fetal alcohol syndrome (FAS), which distorts the facial features (especially the eyes, ears, and upper lip). Later in pregnancy, alcohol is a behavioral teratogen, the cause of fetal alcohol effects (FAE), leading to hyperactivity, poor concentration, impaired spatial reasoning, and slow learning. However, some pregnant women drink alcohol with no evident harm to the fetus.
Low birthweight (LBW) is defined as weight less than 2,500 grams (5 pounds, 8 ounces). LBW babies are further grouped into very low birthweight (VLBW), which is less than 1,500 grams (3 pounds, 5 ounces), and extremely low birthweight (ELBW), which is less than 1,000 grams (2 pounds, 3 ounces).
When compared with newborns conceived at the same time but born later, low-birthweight (LBW) infants are older when they first smile, hold a bottle, walk, and communicate. As the months go by, cognitive difficulties as well as visual and hearing impairments may emerge. Survivors who were high-risk newborns tend to become infants and children who cry more, pay attention less, disobey, and experience language delays. Even in adulthood, some risks persist. Low-birthweight infants have higher rates of obesity, heart disease, and diabetes. The data provide hope as well as caution: Some LBW infants develop normally, overcoming their early problems if they receive excellent early care in the hospital and then at home.
In general, lower socioeconomic classes are more exposed to teratogens than those in other social classes. This may be a result of lack of resources or education or both. The way a culture interprets research varies as well, leading to conflicting recommendations.
At birth, the father’s presence reduces complications, in part because his presence helps the mother during the birthing process. After birth, a father’s support of the new family is crucial, sometimes being the reason for a healthy, happy newborn and mother. From a developmental perspective, some causes of postpartum depression (such as financial stress or marital problems) predate the pregnancy; others occur during pregnancy (especially if the woman is worried about the fetus or birth process); others correlate with birth (especially if the mother is unprepared, alone, or surrounded with unsupportive medical professionals); and still others are specific to the particular infant (health, feeding, or sleeping problems).
Many fathers experience biological symptoms of pregnancy and birth along with their partners. For example, levels of stress hormones correlate between expectant fathers and mothers. Many fathers experience weight gain and indigestion during pregnancy and pain during labor. Paternal experiences of pregnancy and birth are called couvade.
Sometimes the first sign is that the new mother seems euphoric after birth—unable to sleep, or stop talking, or keep from worrying. A crash might follow the high. Overwhelmed by sadness and feelings of inadequacy, a mother suffering from postpartum depression may have trouble caring for her newborn.
The parent–infant bond is the strong, loving connection that forms as parents hold, examine, and feed their newborn. It has been claimed that this bond develops in the first hours after birth when a mother touches her naked baby, just as sheep and goats must immediately smell and nuzzle their newborns if they are to nurture them. While research does not find that early skin-to-skin contact is essential for humans, mother–newborn interaction should be encouraged, although the parent–infant bond depends on many factors in addition to birth practices.
Many studies find that kangaroo-care newborns sleep more deeply, gain weight more quickly, and spend more time alert than do infants with standard care. Infants who experience kangaroo care may adjust to life outside the womb better, and parents who use the method may have increased sensitivity and effectiveness in dealing with the newborn’s needs.