From neighborhoods to housing: heat exposure disparities among pregnant parents and preterm births in Los Angeles County

Abstract Elevated ambient temperatures are associated with preterm birth, which disproportionately occurs among ethno-racially and socio-economically marginalized populations. Existing literature on the reproductive health effects of heat primarily explores ambient temperatures, neglecting individual-level differences in exposure to extreme temperatures due to factors like housing, occupation, and neighborhood land cover. To address these individual differences, we linked 2015–2019 Los Angeles County administrative birth records to 2022 tax parcel data to estimate individual-level housing thermal performance, occupation in high-heat-risk professions, tract-level urban-heat-island intensity, and zip-code-level maximum and minimum ambient temperature exposures among birth parents ( N = 504 761). We use logistic regression to assess disparities in these four heat-exposure metrics by sociodemographic variables previously associated with preterm birth. Black, Latine, Mexican immigrant, and less formally educated parents had consistently higher odds of heat exposure across all four dimensions, relative to their White, US-born Latine, and highly formally educated counterparts. Survival analysis using Cox proportional hazards model indicated that exposure to weeks with an extreme heat day was associated with a 41% (95% confidence interval [CI]: 8%–83%) and 75% (95% CI: 16%–165%) higher hazard of very and extremely preterm births, respectively, relative to pregnancies that did not experience an extreme heat day. We did not find strong evidence for extreme heat exposure and late preterm births. When jointly exposed to poor housing thermal performance and an extreme heat day, the hazard of an extremely preterm birth rose to 177% (95% CI: 15%–567%). We did not find evidence of a joint effect for late or very preterm births. These findings illuminate how housing, occupation, and land cover compound heat-risk exposures among ethno-racially marginalized and socio-economically disadvantaged birth parents in Los Angeles, contributing to preterm birth.