The importance of collecting data which may shed light on the causes of congenital malformations can hardly be overestimated. An accurate determination of incidence may be quite important in the ultimate elucidation of the pathogenesis of these conditions.
Some malformations lend themselves well to incidence determinations. Anencephalus, for example, is fairly easy to detect through vital records. The malformation is characteristic in its appearance, many of the cases are stillborn, and those born alive die within a few days of birth. An analysis of certificates of stillbirth, birth, and infant death in those jurisdictions where malformation information is included on the birth certificate should give fairly complete incidence data. In contrast to this situation are the difficulties associated with studies of the incidence of other malformations. Cardiovascular malformations, for example, are often undetected at birth, may not affect neonatal survivorship, may not manifest themselves clinically, and may be recognized only