Exploring heat risk in pregnant women: do environmental and social inequalities amplify heat exposure?

Heat exposure in pregnancy has been associated with mother-child health. However, characterization of exposure to heat in pregnant women and its associated factors, such as air pollution, vegetation or social stressors, is lacking. We aimed to describe heat exposure according to air pollution and vegetation co-exposures, individual social position and socio-economic context of residence among French pregnant women. We studied 12,235 pregnant women from four mother-child cohorts. Exposure to heat (intensity, duration, severity), particulate matter, nitrogen dioxide (NO₂), ozone (O₃), and vegetation during summer were estimated at the women's residences. Socio-economic context of residence was assessed using the European Deprivation Index (EDI). Cumulative overexposure to heat, air pollution and vegetation were estimated according to reference values. Three profiles of heat exposure, multi-exposure and individual social position, were created using multivariate analysis and unsupervised clustering. Associations of the profiles of heat exposure and multi-exposure with air pollution, vegetation, individual social position and EDI were described using Wilcoxon tests and polytomous regressions. About one-third of pregnant women had a high heat exposure profile combining intense, severe and durable exposure. Depending on the location and year of pregnancy, 27-88% of women were overexposed to heat, air pollution and lack of vegetation. The relationships between profiles of heat and multi-exposure with air pollution, vegetation and individual social position and socioeconomic context of residence depended on the geographical and temporal context. No clear differential exposure pattern across social strata was found. Co-exposure to heat, air pollution and lack of vegetation is common among French pregnant women. Protective measures against summer heat would apply to all pregnant women, as heat exposure represents a universal risk, regardless of socioeconomic status. This research supports future epidemiological studies on combined effects of heat and co-exposures on pregnancy outcomes.