Birth defect is an abnormality in the structure or function of the body that is present at birth. The term birth defect often refers to a body part with a structural abnormality, such as a clubfoot or cleft lip. However, some authorities also consider inherited diseases that don’t produce a visible abnormality, such as phenylketonuria and sickle cell anemia, to be birth defects. Birth defects are also called congenital defects.
There are thousands of known birth defects. Some can be detected immediately at birth. Others become apparent only in later years. Sometimes infants have abnormalities resulting from injury during delivery or from an infection acquired at birth, but most doctors do not consider these abnormalities birth defects.
Birth defects may be major or minor. Major defects are those that usually require medical treatment, often including surgery. Some major birth defects, such as abnormalities of the heart or the respiratory system, can be life threatening. In the United States, approximately 3 percent of all newborn babies have at least one major birth defect. Minor birth defects, such as small birthmarks, often do not require treatment.
Causes.
Physicians do not know what causes most birth defects. However, a specific environmental or inherited cause has been identified for some of them. In many cases, factors relating to the baby’s environment and heredity may work together to produce them.
Environmental causes
are factors outside the fetus that affect its development during pregnancy. For example, some medications can produce birth defects if the mother takes them while pregnant. Certain medical conditions in the mother may also increase the risk of birth defects. For example, if the mother develops rubella early in pregnancy, her baby may have several defects known together as congenital rubella syndrome. Environmental factors appear to have their greatest effect on the fetus during the first three months of pregnancy.
Inherited causes.
Infants may inherit, from one or both parents, certain conditions that result in birth defects. One such condition is Down syndrome, which occurs when the infant inherits an extra chromosome. Some families appear to be at increased risk for having children with certain birth defects, including cleft lip, cleft palate, and spina bifida (a spine defect).
Prevention and treatment.
Because the cause of most birth defects is unknown, doctors often do not know how to prevent them. Avoiding medications that are known to be harmful during pregnancy can prevent some defects. A woman may also prevent certain defects if she follows a proper diet during pregnancy. For example, a woman who takes appropriate amounts of folic acid (a B vitamin) during pregnancy may lessen the chance that her baby will be born with spina bifida.
Genetic counselors can advise couples about their risk of passing a genetic abnormality on to their children. These specialists use medical tests and statistical studies to predict the odds of having a child with a birth defect. For example, Down syndrome occurs more often among infants born to women over age 34, so doctors and genetic counselors commonly advise these mothers about this risk. Some mothers may decide to have an abortion if tests show their baby has a major defect.
Many birth defects can be treated with medications or with surgery. Some defects involving metabolism, such as phenylketonuria, can be treated with a special diet. Some infants with birth defects require other help, including physical therapy and special schooling.
