Dynamic Associations between Ambient PM _2.5 and Its Components and Transitions of Clinical Pregnancy and Adverse Reproductive Outcomes among Participants Treated with ART

Evidence remains unknown regarding the associations between PM2.5 and its components exposure and dynamic progression of different assisted reproductive outcomes in participants undergoing fresh embryo transfer. We included infertile participants at a major assisted reproductive specialist hospital in Chengdu, China, between 2019 and 2022. We conducted multistate modeling and the quantile g-computation approach to explore the association between PM2.5 and its components [black carbon (BC), organic matter (OM), sulfate (SO42–), nitrate (NO3–), ammonium (NH4+) ] and the mixtures with six transitions (from infertility status to clinical pregnancy, from clinical pregnancy to preterm birth (PTB), from clinical pregnancy to miscarriage, from clinical pregnancy to pregnancy complications, from pregnancy complications to PTB, and from pregnancy complications to miscarriage). Mediation analyses were further conducted to explore potential mediating role of reproductive parameters in the associations. Among 11,447 infertile participants with in vitro fertilization, we observed that exposure to higher concentrations of PM2.5 and its components and the mixtures in the 3 months prior to embryo transfer was associated with the progression of the reproductive outcomes, only BC and OM are associated with miscarriage. For example, for each interquartile range increase in OM, the hazard ratios (HRs) were 0.956 [95% confidence interval (CI): 0.927, 0.985] for transition from infertility to clinical pregnancy, 1.176 (95% CI: 1.083, 1.276) for clinical pregnancy to PTB, and 1.115 (95% CI: 1.025, 1.217) for clinical pregnancy to miscarriage. Mediation analysis indicated that the number of high-quality embryos at the cleavage stage accounted for 2.41%, 3.25%, 1.54%, 2.20%, 1.09% and 1.52% of the associations between PM2.5 and its components and clinical pregnancy, respectively. This study provides novel evidence that PM2.5 and its components might play an important role in the progression of assisted reproductive outcomes in infertile participants, particularly in the clinical pregnancy to PTB stage. BC and OM seem to show stronger effects. Additionally, the number of high-quality embryos at cleavage may serve as potential mediators.