From Encyclopedia of Sex and Sexuality
While most babies are born healthy and do not suffer from any obvious genetic or other developmental defects, in about 3 percent of cases the infant is born with a major abnormality. These defects may result from genetic or environmental causes, or from the interaction of both.
Genetic factors are involved in all reproductive processes. Indeed, genetic and chromosomal irregularities are responsible for most known causes of birth defects, and some people run a higher risk of having abnormal children. These include couples who have already produced a child with a genetic disease or birth defect, women over thirty-five years of age and women who have had several miscarriages or stillbirths (babies born dead). A higher risk of birth defects is also associated with race-specific genetic disorders such as sickle-cell anemia in blacks, thalassemia (a form of anemia) in people from Mediterranean areas, or Tay-Sachs disease in Eastern European Jews. Couples in a category of increased risk should seek genetic counseling.
Pregnant women over thirty-five years of age have an increased risk of having a baby suffering from a chromosomal disorder, the most common form of which is Down’s syndrome. The risk of this abnormality increases with maternal age, and older women are counseled to seek a prenatal diagnosis through Amniocentesis or chorionic villi sampling. Amniocentesis involves the drawing of a small amount of fluid for genetic analysis at fourteen to sixteen weeks of pregnancy. A small needle is inserted through the abdominal wall into the uterus to obtain the amniotic fluid, containing cells from the fetus. Chromosomal and other genetic or metabolic evaluation can be performed on these cells to determine if there is an abnormality. Chorionic villi sampling of placental tissue, done through a catheter, allows prenatal diagnosis in the first three months of pregnancy.
During pregnancy, several drugs and other substances can cross the placental barriers and adversely influence the developing fetus. Caution with regard to drug use during pregnancy is recommended, since several drugs may cause developmental defects. Therefore, all pregnant women should consult a physician before using a drug; the potential of a drug to cause malformations of a developing fetus and possible alternative treatments should be discussed. Pregnant women should also be warned about the risk of using “social” drugs—tobacco and alcohol—during pregnancy, since all are associated with birth complications and fetal and infant abnormalities (see fetal and infant substance abuse syndromes; pregnancy and common medications and substances).
Infections are common and potentially dangerous to both the pregnant woman and her fetus. Fetal infections may result in miscarriage, fetal abnormalities, fetal growth retardation, fetal death, or congenital infection. Primary maternal infection with rubella (German measles) during the first three months of pregnancy is a well-known cause of fetal abnormalities, but infections with other viruses such as herpes simplex may cause fetal anomalies as well. Systemic maternal diseases may also cause birth defects. For example, certain forms of diabetes and lupus may cause heart anomalies in the fetus. Women who suffer from such diseases should be carefully screened during pregnancy.