Association between Ambient Air Pollution Exposure and Reproductive Outcomes following In Vitro Fertilization: A Retrospective Cohort Study.

BackgroundAssisted reproductive technologies have become increasingly important in addressing infertility worldwide. Evidence on the associations between ambient air pollution exposure and biochemical pregnancy, clinical pregnancy, and live birth remains limited. Given the widespread exposure to air pollutants and the critical sensitivity of early reproductive processes, understanding these associations is essential for improving clinical outcomes in in vitro fertilization (IVF).Materials and methodsIn this retrospective cohort study, we included 12,453 infertile women who underwent fresh embryo transfer at a major assisted reproductive specialist hospital in Chengdu, China, between 2019 and 2022. Infertility etiologies included a range of female and male factors. Transferred embryos were at the cleavage stage (day 3), graded according to standard morphological criteria, or at the blastocyst stage (day 5), graded according to the Gardner scoring system. Exposure to PM2.5, PM10, O3, and NO2 was estimated at residential addresses using a bilinear interpolation approach applied to the ChinaHighAirPollutants (CHAP) 1 km×1 km gridded dataset. Outcomes included biochemical pregnancy, clinical pregnancy, and live birth, assessed using serum beta-human chorionic gonadotropin (β-hCG) testing, ultrasound confirmation, and delivery records. Associations between air pollutants and outcomes were evaluated using generalized linear models, with estimates reported as odds ratios (ORs) and 95% confidence intervals (CIs), adjusting for key sociodemographic, clinical and paternal characteristics.ResultsAmong the 12,453 participants, 7,548 achieved biochemical pregnancy, 6,550 achieved clinical pregnancy, and 5,601 achieved live birth. Exposure to air pollutants during the period from 85 days before oocyte retrieval to oocyte retrieval (period 4) was significantly associated with decreased odds of all three assisted reproductive outcomes. For live birth, each 10 μg/m3 increase in PM2.5 was associated with a 3.1% reduction in the odds (OR: 0.969; 95% CI: 0.954-0.984).ConclusionOur results provide evidence that ambient air pollution exposure from 85 days before oocyte retrieval to oocyte retrieval is a significant environmental risk factor negatively affecting the biochemical pregnancy, clinical pregnancy, and live birth outcomes in IVF. These findings suggest that reducing exposure to air pollution during critical windows such as gamete development may improve reproductive outcomes.