Time trends (1978-86) of anencephaly and spina bifida in four hospitals affiliated with the International Clearinghouse: a warning.

The prevalence and time trends of spina bifida and anencephaly in the central area of Israel have been studied using data derived from four hospitals affiliated with the International Clearinghouse for Birth Defects Monitoring Systems. Spina bifida rates show a continuous increase from 1978 (1.1/10,000) to 1986 (7.4/10,000) with a peak in 1984 (7-fold increase compared with 1978). The logistic regression analysis of proportion of cases revealed a significant linear trend over time (P less than 0.005). Anencephaly rates increased from 1978 to 1981 but later decreased continuously until 1986 when the prevalence returned to the initial level of 1978. This time trend of spina bifida may represent a real alarm; the implications of this observation are discussed.