Heat Exposure during Pregnancy and Risk of Preterm Birth: A Systematic Review and Meta-Analysis

Abstract

Background: Climate change is increasing the frequency, intensity, and duration of extreme heat events. Pregnant females represent a climate-vulnerable population, yet the relationship between heat exposure during pregnancy and preterm birth has not been consistently synthesized. Objective: To synthesize and critically evaluate the available evidence regarding the association between heat exposure during pregnancy and preterm birth. Methods: A systematic review and meta-analysis were conducted in accordance with PRISMA 2020 guidelines. PubMed and Google Scholar were searched from inception to December 2025 for studies examining the association between heat exposure during pregnancy and preterm birth. Eligible studies included cohort and time-series designs reporting quantitative effect estimates. A random-effects meta-analysis (DerSimonian-Laird model) was used to pool comparable effect estimates. Results: A total of 2,635 records were identified; five studies met the criteria for qualitative synthesis, and four were included in the meta-analysis. The random-effects meta-analysis demonstrated a significant association between maternal heat exposure and preterm birth (pooled RR=1.04, 95% CI: 1.01-1.06; p=0.0119). Statistical heterogeneity was considerable (I²=81.5%). Individual study effect estimates ranged from 1.01 to 1.08 and consistently indicated increased risk. Overall, the included studies were assessed as having low to moderate risk of bias. Conclusion: Heat exposure during pregnancy is associated with a modest but statistically significant increase in the risk of preterm birth. Given the increasing frequency and intensity of extreme heat events associated with climate change, these findings highlight the importance of incorporating maternal health considerations into heat-health action plans, antenatal care guidance, and climate adaptation strategies.