Most pregnancies result in the birth of a healthy infant.
Birth defects, however, remain the leading cause of infant mortality for all races combined, are the fifth leading cause of years of potential life lost, account for 25 to 30 per cent of paediatric admissions, and contribute substantially to childhood morbidity and long-term disability. Major birth defects are those that affect survival, require substantial medical care, or result in marked physiological or psychological impairment. They occur in one to five per cent of live-born infants. The causes of some birth defects have been identified, so that, through effective prenatal counselling and patient education campaigns, we may reduce their incidence. At present time, however, we do not know the cause of more than 65 per cent of birth defects.