The association between ambient air pollution and birth defects in four cities in Hunan province, China, from 2014 to 2016.

This study was performed to assess whether air pollution was positively associated with birth defects and if a specific pregnancy stage played a role. This was a population-based case-control study comprising 153,822 perinatal births in four cities located in Hunan province, China, during the period 2014 to 2016. Exposure to SO2, NO2, and PM10 in each pregnant woman in the first 3 months before pregnancy, and in the first and third trimester was assessed. The risk of birth defects related to SO2 in the first 3 months before pregnancy was between 1.191 and 1.566. In the first trimester stage the risk was between 1.104 and 1.348. The risk of birth defects related to NO2 before pregnancy was 1.285 (95%CI: 1.180-1.399), in the first trimester stage the risk was between 1.280 (95%CI: 1.197-1.368) and 1.380 (95%CI: 1.293-1.473). In the third month before delivery the risk was 1.484 (95%CI: 1.366-1.613). The risk of birth defects related to PM10 in the first month of pregnancy was 1.098 (95%CI: 1.057-1.140), and in the third month before delivery the risk was 1.296 (95%CI: 1.222-1.375). SO2 had a greater effect on the prophase of pregnancy, while NO2 and PM10 had an effect in the late third trimester.