Contribution of prenatal exposure to ambient temperature extremes and severe maternal morbidity: A retrospective Southern birth cohort

BACKGROUNDHealth disparities have persisted in severe maternal morbidity (SMM), an event in which a woman nearly dies from a complication during pregnancy, with limited data on environmental risk factors. OBJECTIVETo examine the association between prenatal exposure to high and low ambient temperatures and SMM during critical windows of pregnancy for a birth cohort in the Southeastern United States. METHODSThis retrospective, population-based birth cohort included hospital deliveries from 1999 to 2017 (570,660 women, 921,444 deliveries). Daily average temperatures at the county- scale were merged with delivery discharge records and days of exposure to very hot and very cold were estimated over the following critical windows: preconception, and first, second, and third trimesters (T1-T3). Generalized estimating equations with multivariable Poisson models examined the association between temperature extremes and SMM for each critical window. RESULTSWomen exposed to a low compared to a high number of cold days during the first and third trimesters were 1.11 (CI: 1.03, 1.20) and 1.30 (CI: 1.20, 1.42) times more likely to experience SMM, respectively. Compared to the no exposure group, women exposed to a high number of very hot temperatures during preconception were 1.09 (95%CI:1.02,1.18) more likely to experience SMM. Sustained exposure to a high or moderate-intensity heat wave during the summer months was associated with a 45% or 39% increase in SMM risk during T2, respectively. Pregnant populations residing in rural locations were more sensitive to cold exposure in T3. Women exposed to a high number of very hot days in T2 compared to no exposure were 20% more likely to experience preterm SMM. SIGNIFICANCEFindings suggest that maternal exposure to hot or cold temperature extremes around the time or during pregnancy may be a contributing environmental risk factor for SMM. More attention should be focused on prenatal counseling in pregnant populations around the risk of thermal extremes. Impact StatementThis is the first study to examine the association between severe maternal morbidity and ambient cold and hot temperature extremes. Results revealed an increase in SMM risk for pregnant individuals following unseasonably cold exposure during the first and third trimesters and exposure to hotter than average temperatures in the second trimester. Our findings suggest that maternal exposure to ambient temperature extremes is a modifiable risk factor for SMM. This study considered contextual social and environmental factors associated with increased SMM risks, such as residential segregation (a proxy for structural racism), residential poverty, and rural compared to urban differences.