The exact cause of most congenital heart defects is not known. But doctors do know that certain things increase the risk that a baby will have a heart defect.

• If the baby's parents or brother or sister has a heart defect, the baby may have inherited a gene from the family that causes a heart problem.
• If the baby's mother drinks alcohol, takes certain prescription or over-the-counter medicines, or uses illegal street drugs during pregnancy, this could cause the baby to have a heart defect.
• If the baby is born prematurely or has a genetic condition such as Down syndrome, he or she has a higher risk of having a heart defect.
• If the baby's mother has diabetes or is exposed to German measles (rubella) during her pregnancy, the baby has a greater chance of developing a heart defect.