Association between ambient temperature exposure and pregnancy outcomes in participants undergoing IVF: a...

To examine the association between ambient temperature and pregnancy outcomes of in vitro fertilization/intracytoplasmic sperm injection and embryo transfer (IVF/ICSI-ET) participants.

We included 10,988 infertile participants who underwent their first IVF/ICSI-ET at a major assisted reproduction specialist hospital in Chengdu, China, between 2019 and 2022. Ambient temperature was assessed using daily mean temperatures from the European Centre for Medium-Range Weather Forecasts Reanalysis v5 (ERA5) dataset, matched to the women's residential addresses, and eight exposure periods were defined based on key stages of IVF treatment. We used a generalized linear model to explore the association between ambient temperature and clinical pregnancy and live birth, constructing dose-response curves to examine non-linearity.

Among the participants, 5,805 (52.83%) achieved clinical pregnancy, 4,979 (45.31%) further achieved live birth. We observed that both low- and high-temperature exposures significantly influence pregnancy outcomes. Specifically, during the clinical pregnancy confirmation period (from serum hCG test to ultrasound test), higher temperatures during cold weather were positively associated with clinical pregnancy rate [adjusted odds ratio (aOR) = 1.017, 95% confidence interval (95% CI) 1.005, 1.030]. During hot weather, increased temperatures were negatively associated with live birth rate. This association was observed during the ovarian stimulation phase (from gonadotropin start to oocyte retrieval) (aOR = 0.887, 95% CI 0.803, 0.980), pregnancy period (from ultrasound test to delivery outcome) (aOR = 0.962, 95% CI 0.950, 0.974), and throughout the entire pregnancy period (from serum hCG test to delivery outcome) (aOR = 0.921, 95% CI 0.909, 0.934). Restricted cubic spline curve results indicated significant nonlinear associations between hot weather during pregnancy and the entire pregnancy period and live birth.

Our study reveals a significant association between IVF treatment outcomes and extreme environmental temperatures, with critical thresholds identified. Exposure to high temperatures during pregnancy (exceeding 21.1 ℃ and 20.8 ℃, respectively) was associated with reduced live birth rates, demonstrating the stage specificity of temperature risks.