Extreme Heat During Pregnancy Raises Serious Health Risks - and Climate Change Is Making It Worse

Heat waves are becoming more frequent, more intense, and longer-lasting as global temperatures rise. Pregnant individuals are among the populations at greatest risk from this shift - a combination of physiological vulnerability and, in many cases, limited ability to avoid exposure through occupational or housing constraints. A review published in JAMA brings together the current state of evidence on this intersection of climate change and maternal health.

What the Evidence Shows About Heat and Pregnancy

The review, authored by Sari Kovats, PhD, of the London School of Hygiene and Tropical Medicine, examines risks from three categories of heat exposure during pregnancy: ambient heat from weather, elevated indoor temperatures in poorly ventilated housing, and occupational heat exposure in jobs that require extended physical activity in warm environments.

Heat stress during pregnancy has been associated with a range of adverse outcomes in existing research. These include preterm birth, low birth weight, stillbirth, and maternal complications including heat exhaustion and heat stroke in cases of severe exposure. The cardiovascular and thermoregulatory demands of pregnancy reduce the body's capacity to dissipate heat, making pregnant individuals more susceptible to heat-related illness at ambient temperatures that would not affect non-pregnant adults at the same level.

The evidence base has expanded significantly in the past decade, driven partly by increasing recognition that climate-related health risks require clinical attention beyond what traditional public health messaging has provided. However, the strength of evidence varies across outcomes. The association between heat exposure and preterm birth, for instance, is supported by multiple large observational studies. Evidence for some other outcomes is less consistent, reflecting differences in study populations, exposure measurement approaches, and the difficulty of controlling for confounding factors in retrospective data.

Occupational Exposure and Indoor Heat

The review pays particular attention to two exposure pathways that receive less public attention than outdoor heat: workplaces and homes. In high-income countries, outdoor workers - in agriculture, construction, and similar sectors - face elevated heat exposure that is difficult to mitigate simply through behavioral change. In low- and middle-income countries, the problem extends to a larger fraction of the workforce.

Indoor temperatures in hot climates or during heat waves can exceed outdoor temperatures in homes without air conditioning, particularly those with poor insulation. The review notes that for many pregnant individuals globally, avoiding indoor heat is not simply a matter of adjusting a thermostat. Housing quality, energy costs, and the absence of cooling infrastructure create structural barriers to heat mitigation.

Management Strategies and Gaps

The review discusses what is currently known about risk management, including hydration, rest in cool environments, modified work schedules during extreme heat events, and the role of health systems in identifying and monitoring pregnant patients at elevated risk. It also identifies gaps: there is limited evidence from randomized controlled trials on specific interventions for heat management in pregnancy, and clinical guidelines in many countries do not yet incorporate specific heat exposure thresholds or response protocols.

The climate trajectory suggests this gap will become more consequential over time. Under most plausible emissions scenarios, heat waves of the intensity that currently occur rarely will occur regularly within decades. Maternal health systems in both high-income and lower-income settings will need to develop protocols that do not currently exist.

The review was published in JAMA (DOI: 10.1001/jama.2026.0001). Correspondence should be directed to Sari Kovats at Sari.kovats@lshtm.ac.uk.