Birth defects are physical abnormalities that are present at birth. They are also called congenital abnormalities. More than 3,000 have been identified.

Birth defects are found in 2-3% of all newborn infants. This rate reaches 10% by age five, as more defects become evident. Almost 20% of deaths in newborns are caused by birth defects.

Abnormalities can occur in any organ or part of the body. Major defects are structural abnormalities that require medical and/or surgical treatment. Minor defects are abnormalities that do not cause serious health or social problems.

The specific cause of many congenital abnormalities is unknown. Any substance that can causes abnormal development of the egg in the mother's womb is called a teratogen. Growth in the uterus is rapid, and each body organ has a critical period in which it is especially sensitive to outside influences. About 7% of all congenital defects are caused by...