Prolonged exposure to extreme heat during pregnancy significantly increases the risk of adverse birth outcomes, with women in West Bengal’s humid subtropical regions facing a heightened threat of delivering low-birth-weight babies, according to a first-of-its-kind population-scale study conducted across India. The research also found that rural, less-educated and socially vulnerable mothers are the most affected, underscoring the need to prioritise pregnant women in India’s heat action plans.
The study, Effect of extreme heat stress on adverse pregnancy outcomes in India, analysed 209,266 births recorded between 2015 and 2020 by matching each pregnancy with local heat exposure. Researchers measured consecutive “sweltering” days—when the India Heat Index exceeded the 90th percentile of the long-term local climate—and found that every additional day of sustained extreme heat increased the odds of a low-birth-weight baby by around one per cent. Heat exposure during the first trimester was linked to a greater risk of preterm birth, while exposure during the second trimester was associated with lower birth weight.
Led by researchers from the University of Queensland–IIT Delhi Academy of Research (UQIDAR), IIT Delhi and the University of Queensland, with collaborators from UNSW Sydney, the University of Exeter and Korea University, the study highlighted a strong social gradient. Mothers with little or no formal education were found to face significantly higher risks of low birth weight and stillbirth as heat exposure increased. Lead author Vineetha Vincent said the findings show that “each additional day of extreme heat a mother endures nudges up the risk to her baby,” while IIT Delhi Professor SagnikDey stressed that adaptation policies must focus on women with the fewest resources to cope with rising temperatures.
The findings are particularly significant for West Bengal, where a large share of the population resides in humid subtropical districts identified by the study as being strongly associated with heat-related low birth weight. Public health experts say the research is likely to strengthen calls for greater investment in maternal healthcare, heat-resilient public health infrastructure, community awareness campaigns and climate adaptation measures across the state. It could also influence healthcare planning and resource allocation as prolonged heatwaves become more frequent under changing climate conditions.