Association between PM_2.5 exposure and the outcomes of ART treatment: A prospective birth cohort study

Exposure to fine particulate matter (PM_2.5) has been reported to be adversely associated with reproductive health. However, current evidence on PM_2.5 exposure adversely influencing pregnancy outcomes remains inconclusive. Women receiving assisted reproductive technology (ART) treatment are under close monitoring with regards to their treatment process, which make them great study population to assess the impact of PM_2.5 in the post-implantation period. Therefore, within a prospective cohort study in Jiangsu, China, we assessed the associations between exposure to ambient PM_2.5 and the outcomes of ART treatment, including implantation failure, biochemical pregnancy loss, clinical pregnancy and live birth, in 2431 women who underwent the first fresh embryo transfer or frozen embryo transfer cycle. High-performance machine-learning model was performed to estimate daily PM_2.5 exposure concentrations at 1 km spatial revolution. Exposure windows were divided into seven periods according to the process of follicular and embryonic development in ART. Generalized estimation equations (GEE) was used to assess the association between PM_2.5 and ART outcomes. Higher PM_2.5 exposure was associated with decreased probability of clinical pregnancy (RR: 0.98, 95 % CI: 0.96-1.00). Each 10 μg/m³ increase in PM_2.5 exposure in the duration from hCG test to 30 days after embryo transfer (Period 7) was positively associated with the risk of biochemical pregnancy loss (RR: 1.06, 95 % CI: 1.00-1.13), and more prominent effects were observed in women undergoing fresh embryo transfer. Null associations were observed between PM_2.5 exposure and implantation failure or live birth at any exposure window. Collectively, our study suggested that exposure to PM_2.5 increased the risk of adverse treatment outcomes in the ART population. Thus, for women opting for ART treatment, particularly those who select fresh embryo transfer cycles, additional evaluation of PM_2.5 exposure before treatment might be of value in decreasing the risk of adverse pregnancy outcomes.