Temperature and heat‐load exposure effects on preterm births: Insights from a population‐based study using distributed lag non‐linear models

OBJECTIVE: Preterm birth presents a substantial health, psychological, and economic burden worldwide. Environmental factors, including temperature fluctuations, are known to influence the risk of preterm birth. This study aimed to investigate the association between high temperatures and heat load and preterm births. METHODS: Using a time-series analysis, we examined data from all births in five Israeli districts between 2010-2016. Meteorological indices were computed for each district. Distributed lag non-linear models (DLNM) incorporating Poisson regression were employed to investigate the associations between these meteorological indices and the daily number of preterm births across various time lags, assessing both short- and long-term associations, adjusting for seasonality, holidays and the general trend. RESULTS: During the study period, 1 216 040 newborns were delivered, of which 89 544 (7.36%) were preterm (<37 weeks) and 11 154 (0.91%) early preterm (<32 weeks). Significant non-linear associations were found between temperature, heat load, and daily preterm births. Acute exposure to a 1°C increase in mean daily temperature 14 days before delivery was associated with a higher risk of preterm birth (relative risk RR = 1.015; 95% confidence interval CI: 1.010-1.019). Similarly, acute exposure to a 1°C increase in maximal heat load 14 days before delivery was associated with elevated risk (RR = 1.018; 95% CI: 1.011-1.026). Cumulative effects over 14 days were substantial: a 1°C rise in mean daily temperature was linked to a 16% increase in risk (RR = 1.160; 95% CI: 1.145-1.176), while a 1°C increase in maximal heat load was associated with a 14% increase (RR = 1.139; 95% CI: 1.125-1.153). Similar associations were observed for heat load, and for early preterm and very low birth weight births; however, these subgroup analyses were based on fewer events and had wider CIs. CONCLUSION: High temperatures and heat load increase the risk of preterm birth over both short- and long-terms. In the context of global warming, these findings may warrant consideration of climate-related risks in maternal health planning and to develop preventive strategies against heat-related pregnancy complications.