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Birth Defects

Birth defects can result from a malfunctioning gene or an environmental stimulus. If the pregnant woman takes in poisonous chemicals or gets infected with a virus, developmental errors can result in birth defects that are not hereditary. Chemicals such as alcohol, drugs, tobacco ingredients, mercury, lead, cadmium, and other poisons; or infectious agents, such as viruses, that cause birth defects are called teratogens. The specific nature of a birth defect depends on which structures are developing at the time of exposure. Most birth defects develop during the embryonic period and are usually more severe than problems that develop later. The critical period for eyes, ears, arms, legs, and the heart is typically the first 3 months (first trimester) of pregnancy, while the critical period for damage to the reproductive system extends across the first and second trimesters of pregnancy. The critical period for the nervous system is all three trimesters. Because of the long critical period for brain development, many kinds of brain damage can result, the most severe during the embryonic and early fetal periods.

Fetal alcohol syndrome (FAS) is a cluster of abnormalities that occurs in babies of mothers who drink alcoholic beverages during pregnancy. Low intelligence, a small head with flat face, misshapen eyes, a flat nose, and thin upper lip characterize children with FAS. Intellectual impairment ranges from minor learning disabilities to severe mental retardation. The more severe mental retardation results from exposure of the embryo/fetus during the early months of pregnancy. Currently, FAS is the leading cause of mental retardation in the United States. Cigarette smoking during pregnancy is associated with miscarriage, stillbirth, premature delivery, and low birth weight. Heroin- and cocaine-exposed fetuses that are born live may undergo withdrawal symptoms, and may be distractable and unable to concentrate. Researchers have difficulty pinpointing other prenatal effects of cocaine and heroin because affected babies are often exposed to additional substances and situations that can account for other symptoms.

Malnutrition and prescription and over-the-counter drugs can cause birth defects. Even certain nutrients ingested in large quantities can be teratogenic. For example, high doses of vitamin A can cause heart, nervous system, and facial defects. Viruses such as rubella can pass into the placenta and cause birth defects. During the first trimester of pregnancy, rubella can cause cataracts, deafness, and heart defects; during later weeks effects include learning disabilities, speech and hearing problems, and Type 1 diabetes.

Behavior of the Neonate

At birth, neonates, or newborn babies, are equipped with basic reflexes that increase their chances of survival. A sequence of rooting, sucking, and swallowing reflexes enables the neonate to get food. Rooting is the neonate’s response of turning his or her head when touched on the cheek and then trying to put the stimulus into his or her mouth. What touches the newborn’s cheek is frequently a nipple. Sucking is the automatic response of drawing in anything at the mouth. Swallowing is a contraction of throat muscles that enables food to pass into the esophagus without the neonate choking. The lack of some reflexes in a neonate can indicate possible brain damage to neuropsychologists. Among those they test are the grasping reflex, when the infant closes his/her fingers tightly around an object put in his/her hand, and the Moro or startle reflex, in which a loud noise or sudden drop causes the neonate to automatically arch his/her back, fling his/her limbs out, and quickly retract them. As the infant matures, developing voluntary control over behaviors, many of the reflexes disappear.

Neonates’ adaptive behavior is not limited to reflexes; they also show behaviors that facilitate social interactions. Shortly after birth, infants respond to the human