Epidemiology of neural tube defects in Utah, 1940-1979.

The prevalence and distribution of 991 cases of neural tube defects who were born in Utah in 1940-1979 are analyzed. The average prevalence at birth is 1.00 per 1000 births (live and stillbirths), which is similar to other states in the western United States. A decline in prevalence is observed during the past 10 years, although there is not a long-term secular trend for the whole time period. Examination of hospital records shows that 17.9% of neural tube defects were not reported on birth or fetal death certificates. The male/female sex ratio is 0.67. No seasonality is found for spina bifida cases; however, a bimodal distribution, with a substantial deficit in May, is observed for anencephaly. A significant negative correlation is found between neural tube defect prevalence and the percentage of individuals in each Utah county who are members of the Mormon Church. No association is found between levels of fallout exposure in Utah and regional variation in neural tube defects, and time-space clustering analysis demonstrates no significant clusters of neural tube defects in Utah.