Table 1_The association of extreme heat and PM2.5 with preterm birth and low birthweight in Florida, United States.docx

AC exposure was estimated using real estate data. Logistic regression was used to estimate adjusted risk ratios (aRR).</p>Results<p>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.</p>Discussion<p>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.</p>