Background
Climate change is increasing the frequency and severity of extreme heat events (EHEs), resulting in increased morbidity and mortality for vulnerable populations. Pregnant people and fetuses are at risk for adverse pregnancy outcomes from EHEs.

Objective
To collate and synthesize existing evidence on the effects of EHE on pregnant people and fetuses and relevant mitigating factors and interventions to inform healthcare providers and other pregnancy-focused audiences.

Methods
A peer-reviewed search strategy was conducted in MEDLINE, EMBASE, Global Health, CAB Abstracts, SCOPUS, and ProQuest Public Health, for empirical studies and reviews published between 2009 and 2023 in English and French. The search strategy focused on terms related to EHEs, exposure, and pregnancy. Health outcomes, risk factors and interventions relating to EHEs (defined based on high ambient temperature thresholds) were reviewed and narratively reported.

Findings
Sixty-eight studies were included (n = 16 reviews; n = 52 empirical studies). Associations between both adverse fetal outcomes (e.g., pre-term birth) and maternal outcomes (e.g., severe maternal morbidities) and EHEs were identified. Pregnant people with low socioeconomic status were found to be more likely to have morbidities. Interventions such as improved clinician support have been proposed by researchers to reduce the risk of poor pregnancy outcomes.

Conclusion
There is an association between EHEs and the development of pregnancy-related morbidity and mortality, mediated by environmental, social and intrinsic individual factors. There are remaining knowledge gaps that have been identified that should be addressed, but more importantly, the synthesis of this evidence highlights the urgent need for interventions such as improved healthcare provider education, and policy interventions to mitigate the health riskscaused by exposure to heat in pregnant populations.