The association between maternal exposure to ambient particulate matter of 2.5 μm or less during pregnancy and fetal congenital anomalies in Yinchuan, China: A population-based cohort study

Background: Few studies from western countries have linked prenatal exposure to ambient particulate matter <2.5 μm (PM_2.5) with increased risk of congenital anomalies. However, the results are mixed. Particularly, evidence is limited for Chinese pregnant women. Methods: In this retrospective cohort study, we matched the data of all pregnant women laboured in public hospitals during 2015–2016 in Yinchuan, a capital city of northwest China and the data of daily average PM_2.5, nitrogen dioxide (NO₂), sulphur dioxide (SO₂) and ozone (O₃) concentrations of the nearest monitor station. We calculated a time-dependent exposure over the entire pregnancy for each woman. We used a time varying Cox proportional hazards model to explore the association between PM_2.5 exposure and the risk of congenital anomalies, after adjusting for individual confounders and other pollutants. Results: A total of 39,386 singleton live births were included in the study, and 530 (1.35%) were with congenital anomalies. An increase of 10 μg/m³ in PM_2.5 exposure over the entire pregnancy was significantly associated with increased risk of congenital anomalies, with hazard ratio (HR) of 1.35 [95% confidence interval (95%CI): 1.16, 1.58]. For subtype analyses, PM_2.5 exposure exhibited a significant association with cardiac anomalies and other unclassifiable anomalies, with HRs of 1.60 (95%CI: 1.24, 2.08) and 1.42 (95%CI: 1.07, 1.89), respectively. The impacts of PM_2.5 exposure on orofacial anomalies and musculoskeletal anomalies were not significant. Conclusion: Our results indicate high concentration of PM_2.5 could increase the risk of congenital anomalies among Chinese, especially for cardiac anomalies. Self-protective measures involving reducing PM_2.5 pollution exposure during pregnancy as well as environmental policies aiming to restrict PM_2.5 emission could be helpful to reduce the burden of cognitional anomalies.