THE RECENT DECLINE IN PREVALENCE OF ANENCEPHALY AND SPINA BIFIDA1

Abstract

An analysis of time changes in rates of anencephaly and spina biflda in Boston, Massachusetts, over the years 1930–1965 is presented. A threefold reduction in prevalence of these anomalies occurred during the period. The reduction occurred predominantly between 1930 and 1945; between 1946 and 1965 prevalence has been uniformly low. The trend was independent of ethnic group, occupational class or parity. The data have also been analyzed for seasonal variation, but no such variation was observed.