Frequency of human congenital malformations.

Birth defects are important health problems. They are the leading cause of infant mortality, the fifth leading cause of premature years of life lost, and important contributors to our nation's chronic disease burden. Researchers have been successful in finding a few causes of birth defects; however, the etiology of the majority of birth defects remains unknown and thus hampers our ability to prevent these diseases. Clinicians who care for patients with birth defects can play an important role in etiologic research by developing good and testable etiologic hypotheses. Epidemiologists must then use these hypotheses and those provided by scientists working with experimental animals to design studies that can test these hypotheses.