Interaction effects of night-time temperature and PM2.5 on preterm birth in Huai River Basin, China

•Evidence of the effects of nighttime temperature extremes on PTB is scarce.•Third trimester nighttime heat and cold increased the risk of PTB and its subtypes.•We found synthetic effects of nighttime temperature extremes and PM2.5 on PTB. Nocturnal temperature is observed increasing with global warming. However, evidence on night-time non-optimal temperature on the risk of preterm birth (PTB) is limited, and the potential interactions with air pollution on PTB has not been well clarified. We therefore conducted a population-based retrospective cohort study to evaluate the effect of night-time temperature extremes on the risk of PTB and its interaction with air pollution. Records of 196,780 singleton births from 4 counties in Huai River Basin (2013–2018) were obtained. Gridded data on night-time temperature were collected from a high-quality Chinese Air Quality Reanalysis dataset. We used a multivariate logistic regression to evaluate the effects of night-time heat and cold exposure on the risk of PTB as well as its subtypes. Potential interactions between night-time temperature extremes and fine particulate matter