Abstract: Objective：The aim of this study is to investigate the association between the exposure to air pollutions during maternal pregnancy and the risk of birth defects. Methods：A population-based case-control study was conducted to analysis the relationship between birth defects and air pollutants. The data of birth defects was collected from 20 hospitals in the six districts of Tianjin. The data used to be compared was also collected from the same hospitals during the same period. The data of the ambient pollutions was offered by Environmental Monitoring Centre of Tianjin（SO2，NO2）. The average density of the air pollutions per month was collected from January 2001 to December 2006 in the six districts of Tianjin. Results：①The exposure air concentration of NO2 in mother delivery of congenital heart diseases in the 3 months before pregnancy and the first trimester is higher than that of the control group. ②Exposure to NO2 during 3 months before pregnancy and periconceptional were positively correlated with limb shortening，while 3 months before pregnancy were positively correlated with multiple means or toe deformity. The concentration of NO2 in the first month of the pregnant will increase the risk of birth defect. There was no significant difference between air pollutant SO2 and birth defects. Conclusions：The concentration of NO2 in 3 months before and after the pregnant will increase the risk of birth defect. Air pollution could have an adverse effect on normal fetal development in early pregnancy.

Key words: Air pollution, Congenital abnormalities, Sulfur dioxide, Nitrogen dioxide, Epidemiologic studies