Impacts of ambient temperature on pregnant women's cardiovascular function and variations related to fetal sex

Rising global temperatures affect maternal and neonatal health, yet the effects on maternal cardiovascular physiology and potential windows of vulnerability remain largely unexplored. We investigated subacute (0-28 days) heat and cold exposure, estimated using a high-resolution spatiotemporal temperature model, in relation to heart rate, hematocrit levels, and repeated systolic and diastolic blood pressure measurements (transformed into gestational age-specific Z-scores, zSBP, zDBP) among 1854 pregnant women from the French EDEN cohort. Distributed lag non-linear models were used to model both cumulative and lagged effects of heat (95th percentile; 20 °C compared to 11 °C) and cold (5th percentile; 4 °C compared to 11 °C). Models accounted for air pollution, vegetation and humidity and were stratified by gestational age and fetal sex. Heat was associated with a sharp decrease in zSBP for up to 10 days after exposure (−0.14 SD [-0.20; −0.08] 95%-CI). Cold was associated with higher hematocrit (0.28% [0.04; 0.51]) and a modest increase in zSBP (0.06 SD [0.02; 0.09]) over 2-6 days after exposure, with zSBP associations observed only in pregnancies with female fetuses. Subacute effects of heat were not modified by gestational age, nor by air pollution and vegetation. This study underscores the role of short-term heat exposure in shaping maternal cardiovascular responses during pregnancy, while suggesting more limited effects of cold exposure, with variations by fetal sex. These results provide insights into the biological plausibility of temperature extremes effects on pregnancy complications. • Examines temperature-related changes in hematocrit, heart rate and blood pressure. • Acute (≤10 days) and subacute (28 days) heat lowers maternal systolic blood pressure. • Acute cold (≤10 days) increases maternal hematocrit. • Acute cold (≤10 days) raises systolic blood pressure in mothers with female fetuses. • Temperature effects persist regardless of air pollution, gestational age, vegetation.