Agricultural chemical use and congenital cleft lip and/or palate.

A case-control study utilizing vital records and ecologic, surrogate exposure measures was conducted in Iowa and Michigan. The study hypothesis anticipated an excess risk of clefts among fetuses exposed during the peak agricultural chemical use period (April through November) coincident with their first trimester of gestation. To examine this hypothesis, multiple regression techniques were used to aid identification of potential confounders; additional analyses, stratified on the potential confounders, were performed using two chemical exposure indices. The major findings of these analyses suggest: (1) an agricultural chemical effect (using the multiple exposure index) controlling for season of conception; (2) no independent effect of season of conception (thus the null hypothesis is not rejected); and (3) little chemical/season interaction. These results imply that if exposures to agricultural chemicals are, in fact, risk factors for clefts, an expanded model that accounts for multiple pesticidal exposures may be more sensitive than consideration of season of exposure, as originally hypothesized.