NO DETERMINANT of an individual's ultimate potential is as important as the normalcy of their development in utero. When confronted with the consequences of severe fetal malformations, the adage "an ounce of prevention is worth a pound of cure" seems worthy of serious consideration. The forfeiture of human potential arising from debilitating birth defects is a tragedy. In contrast, the healthy fetus becomes an infant with superior opportunities to enjoy the benefits provided within the home and the community. During the course of a normal lifetime, the healthy child is likely to contribute to society. Malformed children with extensive physical and mental incapacities often may not have the same opportunities. Some will have anomalies that can be repaired during early childhood. For some, even survival will not be possible. Scientists in reproductive medicine must recognize both the responsibilities and opportunities for preventing or treating fetal malformations. Antenatal diagnostic tests provide