Is mask-wearing hazardous to children? No, the evidence is insufficient.

The existing studies on the relationships of prenatal ambient air pollutants exposure with stillbirth in the Chinese population are very limited and the results are inconsistent, and the susceptible windows and potential modifiers for air pollutants exposure on stillbirth remain unanswered.We aimed to determine the relationships between exposure to ambient air pollutants and stillbirth, and explored the susceptible windows and potential modifiers for air pollutants exposure on stillbirth.A population-based cohort was established through the Wuhan Maternal and Child Health Management Information System involving 509,057 mother-infant pairs in Wuhan from January 1, 2011 through September 30, 2017. Personal exposure concentrations of fine particles (PM2.5), inhalable particles (PM10), sulfur dioxide (SO2), nitrogen dioxide (NO2), carbon monoxide (CO), and ozone (O3) for mothers were estimated based on their residential address during pregnancy using the inverse distance weighted (IDW) method. We used the logistic regression models to determine the associations at different stages of pregnancy with adjustment for confounding factors.There were 3218 stillbirths and 505,839 live births among the participants. For each 100 μg/m3 of CO and 10 μg/m3 of O3 increase in the first trimester (conception to 13+6 weeks), the risk of stillbirth increased by 1.0% (OR = 1.01, 95%CI: 1.00–1.03) and 7.0% (OR = 1.07, 95%CI: 1.05–1.09). In the second trimester (14 weeks–27+6 weeks), PM2.5, PM10, CO, and O3 exposure were closely related to the risk of stillbirth (P＜0.05). In the third trimester (28 weeks to delivery), for each 10 μg/m3 increase in exposure concentrations of PM2.5, SO2, and O3, the risk of stillbirth increased by 3.4%, 5.9%, and 4.0%, respectively. O3 exposure was positively relevant to the risk of stillbirth (OR = 1.11, 95%CI: 1.08–1.14) in the whole pregnancy. Exposure to NO2 was not significantly associated with the risk of stillbirth. Stratified analyses also presented a stronger association among mothers with boy infant, living in rural areas, delivering between 2011 and 2013, and those without gestational hypertension and history of stillbirth.This study provides evidence that maternal exposure to PM2.5, PM10, SO2, CO, and O3 were related to the increased risk of stillbirth. Both the second and third trimesters might be vital susceptible windows for stillbirth. Our findings expand the evidence base for the important impacts of air pollution on fetal growth.