Interaction of extreme temperature events and fine particulate matter components on pregnancy outcomes in women undergoing assisted reproductive technology: A longitudinal study in Eastern China

Accumulating evidence linked extreme temperature events (ETEs) and air pollutants to adverse pregnancy outcomes. However, it is still unclear how ETEs and fine particulate matter (PM_2.5) components interact to affect pregnancy outcomes, especially in women undergoing assisted reproductive technology (ART). This study included 14,326 women undergoing in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI) in China from 2018 to 2020 to assess the independent and synergistic effects of ETEs and PM_2.5 components exposure 1 year prior to oocyte retrieval (Period 1), during ART treatment (Period 2), and during gestation (Period 3). After obtaining high-resolution PM_2.5 components data and calculating apparent temperature (AT) metrics, we evaluated the associations of ETEs, PM_2.5 components with live birth using generalized linear mixed effects models (GLMM). The results showed that prolonged exposure to heatwave (97.5th-3d; OR=0.891, 95 %CI=0.867-0.916) and cold spell (2.5th-3d; OR=0.928, 95 %CI=0.901-0.955) were associated with lower live birth rates, especially during pregnancy stage (Period 3). In addition, with increasing ETE exposure threshold and duration, the adverse effects of each IQR increment in PM_2.5 and its components intensified progressively (Period 3-PM_2.5: 2.5th-4D, OR=0.972; 5th-4D, OR=0.978; 7.5th-4D, OR=0.984; 10th-4D, OR=0.992; 90th-4D, OR=0.972; 92.5th-4D, OR=0.968; 95th-4D, OR=0.968; 97.5th-4D, OR=0.971), and the synergistic effect was observed between ETEs and PM_2.5 components exposure. Subgroup analyses showed that women aged ≥ 35 years (97.5th-4d; OR=0.902, 95 %CI=0.845-0.962), overweight (2.5th-4d; OR=0.945, 95 %CI=0.913-0.978), and less educated (7.5th-4d; OR=0.971, 95 %CI=0.944-0.999) had higher susceptibility to ETEs. Our findings contribute to clarifying that the interaction of ETEs and PM_2.5 components exposure may jointly affect ART pregnancy outcomes, and there is an urgent need to incorporate environmental risk mitigation into clinical guidelines and public health policies to protect vulnerable populations.