Ambient Temperature and Stillbirth: A Multi-Center Retrospective Cohort Study

BACKGROUND Climate change is expected to have adverse health effects, but the association between extreme ambient temperatures and stillbirth is unclear. OBJECTIVES We investigated acute and chronic associations between extreme ambient temperatures and stillbirth risk, and estimated the attributable risk associated with local temperature extremes in the United States. METHODS We linked 223,375 singleton births ≥23 weeks of gestation (2002–2008) from 12 U.S. sites to local temperature. Chronic exposure to hot (>90th percentile), cold (<10th percentile), or mild (10th–90th percentile) temperatures was defined using window- and site-specific temperature distributions for three-months preconception, first and second trimester, and whole-pregnancy averages. For acute exposure, average temperature for the week preceding delivery was compared to two alternative control weeks in a case-crossover analysis. RESULTS In comparison with mild, whole-pregnancy exposure to cold [adjusted odds ratio (aOR) = 4.75; 95% confidence interval (CI): 3.95, 5.71] and hot (aOR = 3.71; 95% CI: 3.07, 4.47) were associated with stillbirth risk, and preconception and first and second trimester exposures were not. Approximately 17–19% of stillbirth cases were potentially attributable to chronic whole-pregnancy exposures to local temperature extremes. This is equivalent to ∼1,116 cold-related and ∼1,019 hot-related excess cases in the United States annually. In the case-crossover analysis, a 1°C increase during the week preceding delivery was associated with a 6% (3–9%) increase in stillbirth risk during the warm season (May–September). This incidence translates to ∼4 (2–6) additional stillbirths per 10,000 births for each 1°C increase. CONCLUSIONS Extremes of local ambient temperature may have chronic and acute effects on stillbirth risk, even in temperate zones. Temperature-related effects on pregnancy outcomes merit additional investigation. https://doi.org/10.1289/EHP945.