Interaction effects of night-time temperature and PM_2.5 on preterm birth in Huai River Basin, China

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 < 2.5 µm (PM_2.5) were examined using the relative excess risk due to interaction (RERI). We found that the risk of PTB was positively associated with third trimester night-time extremely heat and cold exposure, with adjusted OR of 1.898 (95 %CI: 1.655-2.177) and 2.044 (95 %CI: 1.786-2.339). Similar effects were observed for PTB subtypes, moderately PTB (mPTB) and very PTB (vPTB). Synergistic effects (RERI greater than 0) of each trimester night-time temperature extremes exposure and PM_2.5 on PTB were observed. We identified consistent positive interactions between night-time temperature extremes and PM_2.5 on mPTB. No significant interaction of night-time temperature extremes and PM_2.5 on vPTB was found. In conclusion, this large retrospective cohort study found that third trimester night-time heat and cold exposure significantly increased the risk of PTB and its subtypes. There is a synergistic effect between night-time temperature extremes and high PM_2.5 levels on PTB and mPTB. In the context of climate warming, our results add new evidence to the current understanding of night-time non-optimal temperature exposure on PTB.