Extreme temperature events exposure and risks of stillbirths: nationwide large birth cohort study in China.

Extreme temperature events (ETEs) are associated with an increased risk of stillbirth. We conducted a nationwide cohort study based on China Birth Cohort Study (CBCS) across 17 provinces in 2018-2022. A set of cutoff temperature thresholds (2.5th, 5th, 7.5th, 10th, 90th, 92.5th, 95th and 97.5th percentiles of daily apparent temperature of each province during the study period) and durations (at least 2, 3, and 4 consecutive days) were utilized to define 24 distinct ETEs. We show that heatwave exposure was associated with a 36-83% increase in stillbirth. Overall, the adverse impact of cold spells on stillbirths is not significant. The effects varied across regions, and lower population density and greater medical resource were protective factors for the effects. Furthermore, when exposed to ETEs, small vulnerable newborns (SVN) are more likely to experience stillbirth. Our study highlights the need for adaptive and mitigative strategies against ETEs' adverse effects on stillbirth.