BACKGROUND:
Climate Change has wide-ranging, severe health impacts, especially for vulnerable groups. This systematic review and meta-analysis assessed the impact of heat exposure during pregnancy on maternal, fetal and neonatal health.

METHODS:
We conducted a search in MEDLINE (PubMed) and Web of Science in December 2024. Employing Cochrane methodologies on vote counting, narrative synthesis, and meta-analysis, we quantified impacts and graded certainty of the evidence using an adapted IPCC grading.

RESULTS:
The study synthesised data from 229 peer-reviewed articles across 27 health outcomes, predominantly in high-income countries (61.5%). The most studied outcomes were preterm birth (n=102), low birth weight (n=58), hypertensive disorders in pregnancy (n=35) and stillbirths (n=27). Generally, outcomes had a significant number of studies with a positive direction of effect, except for low birth weight, hypertensive disorders in pregnancy, and congenital anomalies, where results were heterogenous. Our results demonstrated increased odds of preterm birth of 1.04 (95%CI=1.03, 1.05) per 1°C increase in heat exposure and 1.22 (95%CI=1.08, 1.37) during heatwaves. Similar patterns were shown for stillbirths and congenital anomalies. Gestational diabetes mellitus odds increased by 28% (95%CI=1.05, 1.74) with higher exposures. Certainty grading revealed very high confidence in preterm birth, high certainty in gestational diabetes and stillbirths, while caesarean sections and neonatal mortality showed very low confidence due to limited evidence and agreement. The review was limited by heterogeneity in heat exposure metrics, outcome measures, and study designs. These differences complicated data synthesis.

CONCLUSIONS:
The findings underscore significant threats to maternal and child health from heat. This highlights the urgent need for robust public health interventions and targeted climate adaptation strategies. This study informs research priorities and the selection of heat-health indicators.