Using individual approach to examine the association between urban heat island and preterm birth: A nationwide cohort study in China

Background: Evidence suggests that maternal exposure to heat might increase the risk of preterm birth (PTB), but no study has investigated the effect from urban heat island (UHI) at individual level.Aims: Our study aimed to investigate the association between individual UHI exposure and PTB.Methods: We utilized data from the ongoing China Birth Cohort Study (CBCS), encompassing 103,040 birth re-cords up to December 2020. UHI exposure was estimated for each participant using a novel individual assessment method based on temperature data and satellite-derived land cover data. We used generalized linear mixed-effects models to estimate the association between UHI exposure and PTB, adjusting for potential confounders including maternal characteristics and environmental factors.Results: Consistent and statistically significant associations between UHI exposure and PTB were observed up to 21 days before birth. A 5 degrees C increment in UHI exposure was associated with 27 % higher risk (OR = 1.27, 95 % confident interval: 1.20, 1.34) of preterm birth in lagged day 1. Stratified analysis indicated that the associations were more pronounced in participants who were older, had higher pre-pregnancy body mass index level, of higher socioeconomic status and living in greener areas.Conclusion: Maternal exposure to UHI was associated with increased risk of PTB. These findings have implications for developing targeted interventions for susceptible subgroups of pregnant women. More research is needed to validate our findings of increased risk of preterm birth due to UHI exposure among pregnant women.