A systematic review and meta-analysis of heat exposure impacts on maternal, fetal and neonatal health.

Climate Change has severe and wide-ranging health impacts, especially for vulnerable groups. Despite growing evidence of heat-associated adverse maternal and neonatal health outcomes, there remains a lack of synthesis quantifying associations and identifying specific risk periods. We systematically reviewed the literature on heat impacts on maternal, fetal, and neonatal health, and quantified impacts through meta-analyses. We found 198 studies across66 countries, predominantly high income (63.3%) and temperature climate zones (40.1%), and 23 outcomes. Results showed increased odds of preterm birth of 1.04 (95%CI = 1.03, 1.06; n = 12) per 1°C increase in heat exposure and 1.26 (95%CI = 1.08, 1.47; n = 10) during heatwaves. Similarly high heat exposure increased the risk for stillbirths (OR = 1.13 (95%CI=0.95, 1.34; n = 9)), congenital anomalies (OR=1.48 (95%CI = 1.16, 1.88; n = 6)), and gestational diabetes mellitus (OR = 1.28 (95%CI = 1.05, 1.74; n = 4)). The odds of any obstetric complication increased by 1.25 (95%CI = 1.09, 1.42; n = 11) during heatwaves. Patterns in susceptibility windows varied by condition. The findings were limited by heterogeneity in exposure metrics and study designs. The systematic review demonstrated that escalating heat exposure poses a major threat to maternal and neonatal health, highlighting research priorities, guiding the selection and monitoring of heat-health indicators, and emphasising the need to prioritise maternal and neonatal health in national climate-health programmes.