The association of extreme heat and PM2.5 with preterm birth and low birthweight in Florida, United States
TL;DR
The results suggest the importance of considering duration and magnitude in defining heat exposure to understand the effects of extreme heat on pregnancy and suggest a need for improved comparability of heatwave definitions as climate change continues to accurately assess their public health impacts.
Abstract
The increase in global temperature due to climate change are leading heatwaves to become more frequent and intense and air quality to worsen. Extreme heat and air pollution have been linked to adverse birth outcomes, which could be mitigated by air conditioning (AC). This study examined associations between heat and PM 2.5 with preterm birth (PTB) and low birthweight (LBW) as well as indicators for AC availability. We used Florida birth certificates to conduct a retrospective cohort study of 4,514,067 births (2000 to 2022). Weather data were obtained from the Parameter-elevation Regressions on Independent Sloped Model and exposure based on mother's residential address. Three heatwave definitions were evaluated based on consecutive days with maximum temperature exceeding 90th percentile. PM 2.5 concentrations (µg/m 3 ) were extracted from the North America Chemical Reanalysis dataset and averaged by trimester. AC exposure was estimated using real estate data. Logistic regression was used to estimate adjusted risk ratios (aRR). We found an increased risk of PTB with increasing heatwave days occurring within a heatwave episode (aRR 1.001, 95% CI 1.001–1.002) during the first trimester and an inverse association in the second (aRR 0.996, 95% CI 0.995–0.997) and third trimesters (aRR 0.921, 95% CI 0.920–0.922). An inverse association with term LBW was observed in the third trimester (aRR 0.981, 95% CI 0.979–0.984). Higher PM 2.5 exposure during the first trimester was associated with increased PTB risk (aRR 1.010, 95% CI 1.008–1.012) and an inverse association with LBW (aRR 0.988, 95% CI 0.984–0.992) with increasing PM 2.5 concentrations in the first trimester. There was no mitigation effect of AC. These results suggest the importance of considering duration and magnitude in defining heat exposure to understand the effects of extreme heat on pregnancy. There is a need for improved comparability of heatwave definitions as climate change continues to accurately assess their public health impacts.