| Objectives: We aimed to examine the association between ambient residential SO2 exposure during pregnancy and missed abortion in Tianjin, an industrial city in northern China.Methods: A population-based case-control study was conducted to investigate the relationship of maternal SO2 exposure and the risk of missed abortion. We selected 927 cases and 879 controls between 2002 and 2006 from a 15-hospital network in six districts of Tianjing. Controls were frequency matched to cases on maternal age (< 20, 20–29, 30-39, >39 years), hospital, the year of pregnancy and the same district of maternal residence.The pollution level have no much difference during the six districts of Tianjing. The cases and controls who work in one of these districts. Maternal exposure to ambient SO2 was estimated based on the time of missed abortion and the last menstrual period, using daily measurement data from the routine monitoring station in the residence district of the pregnant women. Multivariable logistic regression models were used to examine the impact of ambient SO2 exposure on the risk of missed abortion, adjusting previous gravidity history.Results: In the unadjusted model, we observed a statistically significant elevation of risk of missed abortion for women in the fourth (highest) quartile of exposure compared with those in the first (lowest) quartile of exposure (OR = 1.88, 95% CI 1.44-2.44). Pregnant women who exposed during heating period showed 38% higher risk of missed abortion than those during summer and fall (OR = 1.38, 95% CI 1.14 - 1.66). In multi-variable model,After the adjustment for abortion history,product history and age, the risk of SO2 exposure was attenuated and no longer statistically significant.Conclusion:Our results suggest that exposure to ambient SO2 during pregnancy may be adversely associated with incidences of missed abortion ,although the effect of SO2 exposure to missed abortion is weaker than the other factors such as product history.
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