Effect Modification by Ambient Temperature on the Association of Ambient Ozone Exposure with Diet-Controlled and...

Background: Previous studies have explored the association between ambient ozone (O₃) exposure and gestational diabetes mellitus (GDM). However, little is known about the association of O₃ with different GDM clinical classifications-diet-controlled GDM (GDMA1) and insulin-treated GDM (GDMA2), and whether temperature modifies the associations. Methods: We conducted a retrospective cohort study including 11,491 pregnant women between 2017 and 2023 in Tianjin, China. O₃ exposure levels for each participant were assessed using the Tracking Air Pollution in China dataset. Logistic regression models were employed to analyze the associations of trimester-specific O₃ exposure with GDMA1 and GDMA2. Distributed lag nonlinear model (DLNM) was used to identify potential critical gestational weeks of O₃ exposure. Ambient temperature was categorized using the 10th and 90th percentiles to evaluate the effect modification of extreme temperatures on these associations. Results: No statistically significant association was observed in the fully adjusted trimester-specific models. In the weekly-specific DLNM analyses, we observed 5-12 weeks before pregnancy and 26-28 gestational weeks as sensitive windows where O₃ exposure was weakly associated with elevated GDMA1 risk, and 11-25 gestational weeks for GDMA2. Each 10 μg/m³ increase in O₃ during pregnancy was associated with small increases in the odds of GDMA1 (28 weeks: OR = 1.019, 95% CI: 1.002, 1.035) and GDMA2 (25 weeks: OR = 1.018, 95% CI: 1.002, 1.035). High temperatures appeared to strengthen the observed association between preconception O₃ exposure and GDMA1. Additionally, O₃ exposure during pregnancy may increase the risk of GDMA1 among women aged <35 years, preconception obesity, gestational hypertension, and family history of diabetes. Conclusions: This study suggests possible weak weekly-specific associations between O₃ exposure and GDM classifications and indicates that ambient high temperature may modify the O₃-GDM association. These findings should be interpreted cautiously and require confirmation in future studies.