Heat Exposure During Pregnancy and Risk of Preterm Birth: A Systematic Review and Meta-analysis

Background: Preterm birth is a leading cause of neonatal morbidity and mortality worldwide. Concurrently, climate change is increasing the frequency, intensity, and duration of extreme heat events, yet pregnant individuals remain an under-recognized climate-vulnerable population. Although growing evidence suggests that heat exposure during pregnancy may increase the risk of preterm birth, findings have not been consistently synthesized. Methods: We conducted a systematic review and meta-analysis in accordance with PRISMA 2020 guidelines. PubMed and Google Scholar were searched from database inception to December 2025 for observational studies examining the association between heat exposure during pregnancy and preterm birth. Eligible studies included cohort and time-series designs reporting quantitative effect estimates. Risk of bias was assessed using the Newcastle–Ottawa Scale. A random-effects meta-analysis was performed to pool comparable effect estimates. Results: A total of 2,635 records were identified, of which seven studies met the inclusion criteria for qualitative synthesis and four studies were included in the final meta-analysis. All studies included in the quantitative synthesis reported positive associations between heat exposure during pregnancy and preterm birth, with adjusted hazard ratios, odds ratios, or relative risks ranging from 1.01 to 1.08. Despite heterogeneity in exposure definitions and study settings, the direction of association was consistent across studies. Overall, the included studies were judged to have low to moderate risk of bias. Conclusions: This systematic review and meta-analysis provides evidence that heat exposure during pregnancy is associated with an increased risk of preterm birth. As climate change continues to intensify global heat exposure, integrating maternal health considerations into heat–health action plans and climate adaptation strategies is essential to reduce preventable adverse birth outcomes.