Disproportionate climate burden of rising temperatures on low birth weight in Pakistan.

backgroundWarming temperatures add to the global health burden, with disproportionate effects on pregnant women and newborns. Low birth weight is a major neonatal health issue in Pakistan, leading to neonatal mortality and impaired long-term health. We assessed the impact of extreme temperatures on low birth weight, identified high-risk subgroups, estimated the heat-attributable burden, projected future risks, and constructed a district-level heat vulnerability index.

methodsWe conducted a space-time series study using nationally representative surveys from 2008 to 2017 across Pakistan's provinces. We modelled temperature-low-birth-weight associations with distributed-lag non-linear models in a generalised mixed-effects framework, with model averaging to address specification uncertainty. Subgroup analyses considered maternal education, household wealth, urban/rural residence, and air quality. We estimated heat-related population attributable fraction using observed temperature and projections under SSP2-4.5 and SSP5-8.5. Province-level risk estimates combined with district-level indicators, such as mean temperature, multidimensional poverty, and under-5 mortality, were used to develop the heat vulnerability index.

resultsThe study included 85,017 participants, with 15,920 (18.72%) infants identified as having low birth weight. Heat-related risks for low birth weight varied across provinces, with relative risks ranging from 1.47 (1.07-2.03, 95% confidence interval) to 1.91 (1.24-2.93) at the 99th percentile of temperature. The heat-related population attributable fraction ranged from 9.39% to 13.15%, translating to 1.24 million heat-related low-birth-weight cases over the study period. Projections indicate that heat-related population attributable fractions will increase by 8.43-10.20% by the 2060s. Subgroup analysis showed higher risk among women exposed to hazardous air pollution, those with less education, and urban residents. Women in southern Punjab, northern Baluchistan, and Sindh faced the highest risks.

conclusionsOur findings identify Pakistan's districts most vulnerable to heat-related low birth weight and highlight contributing factors. These insights can inform targeted interventions to mitigate risks. The study advances the understanding of the impacts of rising temperatures, particularly in resource-limited and high-risk settings.