Congenital heart disease is a general term that refers to defects of the heart that occur during the development of the fetus. They are present at birth but may be discovered much later. The exact causes of congenital heart disease, which occurs in about 0.8% of live births, is unknown. Approximately 10% of all congenital cardiac defects can be accounted for by chromosomal aberrations or genetic mutations or transmission. Down syndrome is the most common chromosome aberration and occurs in about 1 in every 700 births; the risk rises steeply if the mother is over age 35 and is as high as 4% for women over age 44. In this condition, an atrial septal defect (ASD), a hole in the septum dividing the top chambers of the heart is common.
Congenital defects associated with prenatal exposure to teratogens, which adversely affect embryonic or fetal development, include infectious vectors such as rubella, and drugs and chemicals including radiation, ACE inhi¬bitors, alcohol, hydantoin, lithium, phenylalanine, thali¬domide, trimethadione, valproic acid, vitamin D, and anticoagulants as well others. Because so little is known about the causes of the majority of congenital heart defects, and teratogens are strongly implicated in many, it must be emphasized that no medication should be taken during the first six months of pregnancy without prior consulta¬tion of a knowledgeable physician.

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