A congenital disorder is a medical condition that is present at birth. (It is contrasted with the term "acquired disorder") A congenital disorder can be recognized before birth (prenatally), at birth, or many years later. Congenital disorders can be a result of genetic abnormalities, the intrauterine environment, or unknown factors. A congenital condition can arise from the genetic make-up of the fertilized egg or be acquired at any time during fetal development. The causes of many congenital disorders are not known. Congenital disorders include minor physical anomalies (e.g., a birthmark), severe malformations of single systems (e.g., congenital heart disease or amelia of the legs), and combinations of abnormalities affecting several parts of the body. Defects of metabolism are also considered congenital disorders. A congenital disorder can have trivial or grave effects. The most severe, such as anencephaly, are incompatible with life. Birth defects are a leading cause of death in early infancy, accounting for the deaths of nearly 2 out every 1000 infants (US statistics).
About 2% to 3% of babies are born with significant congenital birth defects. Birth defects involving the brain are the largest group at 10 per 1000 live births), compared to heart at 8 per 1000, kidneys at 4 per 1000, and limbs at 2 per 1000. All other defects have a combined incidence of 6 per 1000 live births. Birth defects of the heart are the most common birth defect leading to death in infancy, accounting for 28% of infant deaths due to birth defects, while chromosomal abnormalities and respiratory abnormalities each account for 15%, and brain defects about 12%.
About 25% of birth defects result from genetic abnormalities. About 5% involve abnormalities of large portions or entire chromosomes. Some congenital disorders arise from inheritance of abnormal genes from the parents, but some can arise from a new mutation in one of the germ cells that contributed to the fetus.