Maternal Exposure to Surface Ozone and Reduced Fecundity in China: Evidence from a Nationwide Survey

The influence of ground-level O₃, which possesses a higher oxidative concentration than other ambient pollutants, on reproductive health has received relatively limited scrutiny. In this study, we collected information on reproductive history, sociodemographic profiles, lifestyle, and residential details of 10,153 couples at risk of pregnancy. Each participant's 1-year, 3-year, and 5-year average O₃ exposure levels were estimated using a previously developed randomized trees model. We used discrete-time Cox proportional hazards models to estimate the fecundability odds ratio (FOR) for each 10 μg/m³ change in the O₃, adjusting for a set of demographics, lifestyle, and environmental covariables. We observed that a 10 μg/m³ increase in the annual average level of exposure to O₃ was associated with a 16% reduction in fecundity (FOR: 0.84; 95% CI: 0.82-0.85). We also observed a 40% increase in the odds of infertility (OR: 1.40; 95% CI: 1.34-1.46) for each 10 μg/m³ rise in the annual mean of O₃ exposure. After adjustment for fine particulate matter, the strong association between O₃ exposure of fecundity to O₃ persisted. Given the increasing epidemic of infertility, we strongly advocate for heightened consideration of O₃'s impact on reproductive health, as it may partially counterbalance the health benefits gained from improved PM_2.5 levels in a middle-income setting.