A ten-year study of anencephaly.

The incidence of anencephaly at the Los Angeles County General Hospital during the period of July, 1948 through June, 1958 was 0.049 per cent. Worldwide the range of reported incidence is 0.012 per cent to 0.671 per cent. In this study 65 per cent of the total number of anencephalics delivered were females, a predominance agreeing with reports by other investigators. Polyhydramnios appeared in 38 per cent of the anencephalic pregnancies of this study, while 15 per cent of the deliveries were complicated by placenta praevia.A significant number (48 per cent) of the multiparae gave a history of previous stillbirths or abortions. The present study does not support observations by other investigators which indicated an increase in anencephalic births during the winter months. Evidence from stillbirth statistics would seem to indicate that anencephaly is primarily a genetically induced phenomenon. Further evaluation and analysis of the predominance of females in anencephalic stillbirths and abortions is suggested, in order to study whether the observed secondary or birth sex ratio (in which males predominate) is, in fact, due to genetic effect.