Heat exposure and adverse birth outcomes: Modification by residential greenness in a 14-year prospective cohort study in Taiwan

Background: Pregnant women are vulnerable to climate change, with high ambient temperature (AT) associated with adverse birth outcomes. Inconsistent study designs, limited metrics, and unclear roles of greenness as an adaptation strategy hinder region-specific climate policies. This study assessed the effects of prenatal heat exposure on birth outcomes and whether greenness moderates this association. Methods: Participants were recruited from the ongoing Longitudinal Examination Across Prenatal and Postpartum Health in Taiwan project, initiated in 2011. Birth outcomes were analyzed from 2011 to 2024. Heat exposure was defined as mean daily AT and wet-bulb globe temperature (WBGT) exceeding the 95th percentile across trimester stages, and birth outcomes were obtained from Children's Health Booklet records. Residential greenness was assessed using the normalized difference vegetation index. General linear and logistic regression models were applied. Results: A total of 1478 births were analyzed. Exposure to extreme heat during late or the entire pregnancy was associated with a reduced gestation period (AT in late pregnancy: β = −0.60, 95 % CI: −0.98, −0.23; WBGT in entire pregnancy: β = −0.75, 95 % CI: −1.19, −0.31) and increased risk of preterm birth (AT in late pregnancy: OR = 3.08, 95 % CI: 1.45, 6.53; WBGT in entire pregnancy: OR = 3.35, 95 % CI: 1.39, 8.06). High WBGT in late pregnancy predicted low birth weight. These effects were more pronounced during the hottest and coldest months and in areas with low residential greenness, suggesting a protective role of green space. Conclusions: High AT and WBGT during pregnancy are associated with shorter gestation, lower birth weight, and elevated risks of preterm and low birth weight, particularly in late pregnancy. WBGT is a useful indicator of heat exposure. Greenness helps mitigate the aforementioned effects, underscoring the importance of residential environments. Our findings offer key insights for public health and urban planning.