Heat waves and early birth: Exploring vulnerability by individual‐ and area‐level factors

We examine associations between acute heat wave exposure and risk of preterm (PTB) (28–36 weeks) or early term (ETB) (37–38 weeks) birth, stratified by individual‐level and area‐level factors. Daily ambient mean temperature was linked to maternal residence in state vital records for preterm and early term births in California, Florida, Georgia, Kansas, Nevada, New Jersey, North Carolina, and Oregon between 1990 and 2017.

Heat waves were identified during the four‐day exposure window preceding birth using the 97.5th percentile mean temperature for zip code tabulation areas (ZCTA). We used a time‐stratified case‐crossover design, restricted to the warm season (May through September) and stratified by maternal age, maternal education, ZCTA‐level impervious land cover or social deprivation index. We pooled estimated odds ratios across states using inverse‐variance weighting.