Identifying the critical windows and joint effects of greenness and particulate matter exposures for preterm birth: a retrospective study across Guangdong Province in China from 2014 to 2018.

Background: Green space may have a wide range of beneficial health effects, but its association with preterm birth (PTB) remains inconclusive. Therefore, our study aims to investigate the effect of green space and its joint effect with particulate matter (PM) on PTB. Additionally, we seek to identify its critical susceptibility window.

Methods: This retrospective study included 5,240,828 pregnant women in Guangdong Province from 2014 to 2018. Due to clustering among pregnant women, generalized estimating equations were used to examine the effects of green space and its joint effect with PM pollution on PTB, by using the normalized difference vegetation index (NDVI) and the fraction vegetation coverage (FVC) within 500 m and 1,000 m.

Results: Green space can effectively reduce PTB risk, particularly in the first trimester. The odds ratio for PTB associated with NDVI throughout the pregnancy was 0.80 (95% CI: 0.70, 0.92) within 500 m and 0.81 (95% CI: 0.70, 0.93) within 1,000 m. When accounting for joint effects, high green space combined with low PM levels had the strongest protective effect, especially in the third trimester. On the other hand, the association between the FVC and PTB was similar to that between the NDVI and PTB. Additionally, green space helped mitigate PTB risk even in the areas with higher PM concentrations.

Conclusions: Our finding enables us to create targeted approaches to increase exposure to green space during pregnancy. Furthermore, green spaces should be considered a beneficial factor in the decision-making process.