Individual ambient ozone exposure during pregnancy and adverse birth outcomes: Exploration of the potentially vulnerable windows

Background: Ambient ozone (O3) exposure during pregnancy might be associated with preterm birth (PTB) and low birth weight (LBW); however, existing evidence remains inconclusive. It is necessary to explore the relationships and potential susceptible periods further. Methods: To explore the relationship between O3 exposure and adverse birth outcomes, a study using records of 34,122 singleton live births in Beijing between 2016 and 2019 was conducted. The O3 exposure in each gestational week of pregnant women was estimated, and Cox proportional hazard models were used to estimate the hazard ratios (HRs) and corresponding 95% confidence intervals (CIs). Distributed lag nonlinear model (DLNM) incorporated in Cox proportional hazard models were used to explore potential critical windows.Results: An increase of 10 mu g/m3 in O3 exposure was associated with a 3.9% (95%CI: 0.6-7.3%) higher risk of PTB. Additionally, this increase in O3 exposure was positively linked to PTB during the 2nd 7th, 22nd 29th, and 37th gestational weeks, and LBW during the 2nd 7th, 24th 29th, and 37th gestational weeks.Conclusions: This study demonstrates a positive correlation between O3 exposure and PTB, and identified specific sensitive periods during pregnancy when the risk was higher.