Prenatal exposure to heat stress and postpartum depressive symptoms in the MADRES cohort in urban Los Angeles

While extreme temperatures have been linked to adverse mental health outcomes, the impact of prenatal heat stress on postpartum depression remains understudied. We evaluated associations between prenatal heat stress and depressive symptoms one year postpartum, identified susceptible gestational windows, and assessed whether neighborhood climate vulnerability modifies maternal susceptibility to heat-related postpartum depression. We included 275 predominantly low-income Hispanic/Latina participants in the MADRES cohort. Residential wet bulb globe temperature (WBGT), is more reflective of physiological responses to heat stress compared to temperature alone, and was estimated throughout pregnancy at residential addresses. Depressive symptoms at 12 months postpartum were assessed using the Center for Epidemiologic Studies-Depression (CES-D) scale. The Climate Vulnerability Index (CVI) was linked at census tract level. We used multivariable linear regression to estimate associations between trimester-specific heat stress and log-transformed CES-D scores and examined effect modification by CVI (≥75th vs. <75th percentile). Distributed lag models (DLM) were used to identify susceptible exposure windows to WBGT, and Bayesian distributed lag interaction models (BDLIM) were used to assess differences in associations by CVI. We found that each interquartile range increase (IQR) in first-trimester WBGT was associated with a 18.93 % (95 % CI: 0.03 %-41.75 %) increase in postpartum CES-D scores. Neighborhood-level CVI modified second-trimester effects of heat stress on postpartum depressive symptoms, with participants in high-CVI neighborhoods experiencing stronger positive associations (31.21 %, 95 % CI: -11.80 %-95.21 %) compared to those in low-CVI neighborhoods (-16.70 %, 95 % CI: -32.29 %-3.55 %) for WBGT. These findings provide novel evidence linking early-pregnancy heat exposure to postpartum depression risk, with effects amplified in climate-vulnerable neighborhoods during mid-pregnancy. Our results suggest that heat mitigation strategies, including providing heat-health education during prenatal visits, may be important for postpartum mental health.