Maternal exposure to sulfur dioxide and the risk of oral clefts in Liaoning Province, China: a population-based case-control study.

There is limited and equivocal epidemiological evidence relating to the association between maternal sulfur dioxide (SO2) exposure and the risk of oral clefts (OCs) in offspring. We performed a population-based case-control study in Liaoning province to evaluate aforementioned relationship during 3 months before conception, the first trimester of pregnancy, and their single months. The study involved 3086 patients with OCs and 7950 controls. Data relating to SO2 concentration was acquired from air monitoring stations throughout the study period. We used a multivariable logistic regression model to evaluate the association between exposure to SO2 and the risk of OCs during the exposure windows. Maternal SO2 exposure was positively related to OCs during the 3 months before conception (odds ratio = 1.38, 95% confidence interval: 1.15-1.65; P for trend < 0.01). Positive relationships were obtained from the first and second months before conception and the first month of pregnancy. Thus, our research reflects a relationship between SO2 exposure and the risk of OCs. Future studies are now required to verify the association between SO2 exposure and OCs during pregnancy and indicate the most relevant vulnerable exposure time windows.