Combined effects of extreme cold events and fine particulate matter on the success rate of in vitro fertilization-embryo transfer: A multi-center retrospective cohort study in China.

As climate change intensifies, the rising frequency of extreme cold events (ECEs) and the known effects of fine particulate matter (PM2.5) on reproductive health highlight a gap in understanding their combined impact on in vitro fertilization-embryo transfer (IVF-ET) success rate. We conducted a multicenter retrospective cohort study in China to explore the association between ECEs and the risk of clinical pregnancy failure (CPF) undergoing IVF-ET, and the combined effects of ECEs and PM2.5 on CPF risk. The study included a total of 96,623 women undergoing IVF-ET, including 40,798 women undergoing fresh embryo transfers and 55,645 women undergoing frozen embryo transfers, with CPF rates of 48.1 % and 46.6 %, respectively. Our results showed that ECEs exposure were positively associated with CPF risk in women undergoing fresh embryo transfer, with the maximum relative risk (RR) of 1.05 (95 % CI: 1.02, 1.08). Furthermore, combined exposure to ECEs and high concentration of PM2.5 further increased the risk of CPF, with the RR of 1.07 (95 % CI: 1.03, 1.11). However, there was no significant association between ECEs and CPF risk in women undergoing frozen embryo transfer. Similarly, no association was found between the combined exposure to ECEs and high concentration of PM2.5 and the CPF risk. Our study provided novel evidence for the adverse effects of ECEs, and the combined exposure to ECEs and PM2.5 on IVF-ET success rate.