Heatwaves and neonatal outcomes beyond preterm birth and low birth weight: A scoping review

BackgroundClimate change is increasing the frequency and intensity of heatwaves globally, with potential implications for maternal and neonatal health. While associations between heat exposure and preterm birth (PTB) and low birth weight (LBW) have been documented, the broader spectrum of neonatal morbidities remains incompletely characterized. This scoping review systematically maps the evidence on heatwaves and neonatal outcomes beyond PTB and LBW.ObjectivesTo identify and synthesize evidence on (1) which neonatal morbidities beyond PTB and LBW are studied in relation to heat exposure; (2) exposure windows examined (preconception, trimester-specific, peripartum); and (3) heat metrics employed in the literature.MethodsFollowing PRISMA-ScR guidelines and the JBI Population-Concept-Context (PCC) framework, we searched PubMed, Embase, Web of Science, and Scopus for peer-reviewed studies examining maternal heat exposure during pregnancy and neonatal outcomes in the first 28 days of life other than PTB and LBW. Because this was a scoping review of a heterogeneous literature, we retained variation in study design, exposure metrics, and outcome definitions rather than attempting quantitative pooling. Two reviewers independently screened titles, abstracts, and full texts. Data were extracted on study characteristics, neonatal outcomes, exposure windows, and heat metrics. Risk of bias was assessed using design-appropriate tools.ResultsFrom 165 initial records, 15 records informed the review. The evidence base was heterogeneous in design, exposure assessment, and outcome definition, and represented 62,986,500 participants across nine countries (primary study publication period: 2012-2020). Eight neonatal outcome categories were identified: mortality (n = 7 evidence sources), NICU admissions (n = 5), thermoregulation disorders (n = 4), metabolic complications (n = 4), respiratory morbidity (n = 3), clinical assessment/Apgar scores (n = 3), congenital anomalies (n = 3), and infectious complications (n = 2). Third-trimester exposure was most frequently studied (n = 9), followed by peripartum (n = 3), second trimester (n = 2), and first trimester (n = 2). Heat metrics included maximum temperature (n = 5), heat index (n = 4), heatwave definitions (n = 4), mean temperature (n = 4), apparent temperature (n = 2), humidex (n = 1), and WBGT (n = 1). Seven studies (47%) were rated as low risk of bias. Across outcome groups, the literature generally suggested adverse associations with heat exposure, but the magnitude, statistical significance, and certainty varied across designs and metrics.ConclusionsThis scoping review reveals a growing, yet heterogeneous, body of evidence linking heat exposure to diverse neonatal morbidities beyond PTB and LBW. Third-trimester and peripartum exposures appear especially relevant, but conclusions should remain cautious because the included evidence varies in design, exposure metrics, outcome definitions, and confounder control. Standardization of heat metrics and exposure assessment is needed. Gaps include limited research on preconception and first-trimester exposures, metabolic and infectious complications, and research from low- and middle-income countries. Future research should employ consistent methodologies and examine vulnerable populations to inform climate adaptation strategies for maternal-neonatal health.