Synergistic effect of exposure to ambient ozone and fine particulate matter on embryonic developmental outcomes among an assisted reproductive population

Air pollution such as fine particulate matter (PM_2.5) may be linked to the increasing prevalence of infertility. However, evidence on the effects of air pollution on embryonic developmental outcomes in populations undergoing assisted reproductive technology (ART) remains limited. Herein, a total of 17 941 couples of patients who underwent <i>in vitro</i> fertilization (IVF) in the reproductive center of the hospital between January 2017 and December 2021 were included. The exposure of couples to PM_2.5 and ozone (O₃) was estimated based on the Tracking Air Pollution in China and their geographic coordinates. Generalized additive models and segmented linear regression analyzed the associations between PM_2.5/O₃ exposure and embryological outcomes, including synergistic interactions. The results revealed that exposure to PM_2.5 and O₃ was significantly negatively associated with normal fertilization rates, high-quality embryo rates, and blastocyst formation rates. PM_2.5 and O₃ exhibited interactive effects in their negative impacts on high-quality embryo rates and blastocyst formation rates. Subgroup analyses revealed that both ambient ozone and PM_2.5 exposures were consistently associated with reduced high-quality embryo and blastocyst formation rates across multiple maternal age and BMI categories, particularly among younger and normal-weight women. Significant interaction effects between ozone and PM_2.5 were observed primarily in women aged < 35 years and those with BMI < 24 kg m^-2, indicating heightened vulnerability in these groups. These findings emphasize the coordinated control of O₃ and PM_2.5 levels to mitigate adverse effects on embryonic development.