Nature Medicine (2024), 05 Nov Lakhoo, Brink, Radebe et a

How Heat Exposure Threatens Maternal And Neonatal Health

With year-on-year record-breaking global temperatures, the health risks for vulnerable populations—especially pregnant women and newborns—are increasingly concerning. Our recent study, published in Nature Medicine, titled "Systematic review and meta-analysis of heat exposure impacts on maternal, fetal, and neonatal health," provides a comprehensive synthesis of the published literature to date, quantifying the risks and specific periods of susceptibility associated with heat exposure during pregnancy.

The Urgency Of Research In Climate-Health Impacts

Despite a growing body of literature, research synthesising the impacts of heat exposure on maternal and neonatal health has been limited. Our study aims to bridge this gap, providing insights into how heat exposure increases the risk of maternal, fetal and neonatal outcomes.

We found 198 studies that assessed the impact of heat on maternal, fetal, and neonatal health, across 66 countries. Most studies were conducted in high-income countries and temperate climate zones (Figure 1). The most studied outcomes were preterm birth and low birth weight.

Figure 1: Geographical and climate zone distribution. Distribution of 198 studies by a) country and b) annual mean temperature

Methodology

We conducted a systematic review, the highest level of evidence, combining the findings of various smaller studies. We utilised various methodologies to summarise the data, including vote counting, narrative synthesis, summary of effect estimates and meta-analyses. We grouped the outcomes in 23 categories (Figure 2).

Figure 2: Summary of direction of effect for each outcome.

Key Findings

When doing meta-analysis, we found that for every 1°C increase in heat exposure, there was a 4% increase in preterm birth risk across all the studies. During a heatwave, the risk of preterm birth increased by 26%. Similarly, we found marked increases in other adverse outcomes such as increased risk for gestational diabetes, stillbirths, congenital anomalies and obstetric complications with increasing exposure to heat. There is limited research on outcomes like antenatal bleeding and caesarian section risks that may be related to heat exposure and could contribute significantly to morbidity and mortality.

A Call For Action

This study highlights the growing, widespread impact of heat exposure on pregnant women and newborns. These insights are key for identifying indicators that could be used to monitor the burden of heat-related health impacts and the effectiveness of adaptations. By identifying specific outcomes, at-risk periods, and by quantifying impacts, our findings serve as a critical tool for both clinicians and policymakers working to mitigate climate impacts on health. Pregnant women and neonates must be prioritised in climate change action.

This study also highlights the research gaps in the low- and middle-income countries and tropical climate zones, where the impacts may be even greater. While the studies originated from 66 countries across diverse climate zones, there was a significant proportion of those from high-income countries and temperature climate zones. We need more evidence from the most vulnerable groups, living in low- and middle-income countries and in tropical climate zones.

Our findings likely underestimate the effects, as the most vulnerable populations are not represented in the data. Higher risks for preterm birth in these groups, particularly those in low-income countries, indicate a critical need for targeted interventions in these populations. Additionally, data on high-risk subgroups—such as individuals with lower socioeconomic status—are scarce, as is research on less common but important health outcomes like mental health effects and hospital admissions.