Objective  To investigate the relationship between exposure to nitrogen dioxide (NO₂) during all stages of pregnancy and the risk of preeclampsia.

  Methods  We collected data on 63 625 pregnant and parturient women having their deliveries between 2015 and 2017 in 10 hospitals covered by the Pregnant and Parturient Women Surveillance System in Shijiazhuang, Chengde and Zhangjiakou city of Hebei province and then divided the women into a preeclampsia (PE) group and a non preeclampsia (non PE) group based on their medical history; the monitoring data on ambient air quality of the three cities during the 3-year period were collected simultaneously. Exposure to NO₂ during pregnancy and in different cities among the two groups of the women were described and compared. Logistic regression model was adopted to analyze the impact of NO₂ exposure on preeclampsia incidence.

  Results  Among all the women, significantly higher NO₂ exposure during pregnancy in PE group (n = 2 006, 3.2%) than that in non PE group (n = 61 619, 96.8%) was observed. The women in Shijiazhuang city had obviously both a higher NO₂ exposure and an incidence rate of preeclampsia compared to the women in other two cities, suggesting that exposure to NO₂ during all stages of pregnancy could increase the risk of preeclampsia. The risk of preeclampsia increased by 1.168, 1.105, and 1.293 times with an increment of 10 μg/m³ in NO₂ exposure during early, middle and late of pregnancy, respectively (P < 0.001). Other risk factors for preeclampsia included at an elder age, at a young age, with a low education, and having a pregnancy in cold season.

  Conclusion  Exposure to NO₂ in all stages of a pregnancy is a risk factor for preeclampsia and pregnant women with the exposure and other risk factors should pay an attention to prenatal examination.