Associations of residential greenness exposure during early pregnancy with the risk of spontaneous abortion: The China Birth Cohort Study

Background: Living in higher greenness level community has many benefits for pregnancy outcomes, however, few research have explored the relationship between greenness and spontaneous abortion (SAB). We aimed to analyze relationships between SAB and community greenness in Chinese pregnant women, and further assessed the modifying effects from air pollutants. Methods We studied 90 890 pregnant women from the China Birth Cohort Study from February 2018 to December 2021. We diagnosed SAB by certified obstetricians and gynecologists. The level of exposure to greenness during the first trimester was measured using the normalized difference vegetation index (NDVI) and the enhanced vegetation index (EVI). Particulate matter ≤ 2.5 µm (PM 2.5 ), nitrogen dioxide (NO 2 ) and ozone (O 3 ) were used as proxies of ambient air pollution. Logistic regression models were used to analyses the association between SAB and greenness. We additionally performed subgroup analyses stratified by age, urbanicity, and air pollution levels. Results Lower SAB prevalence was related to living in greener places. A 0.1 unit increase in NDVI 500m and EVI 500m was significantly associated with a 12.0% (95%CI: 8.6%, 15.3%) and 15.4% (95%CI: 10.5%, 19.9%) lower risks of SAB, respectively. In sensitivity analysis, these relationships remained consistent. The associations were stronger among urban dweller, older and participants lived in places with lower NO 2 and O 3 levels. Conclusions Our findings indicate significantly inverse associations between community greenness and SAB in Chinese pregnant women, especially for urban dweller and older, the NO 2 and O 3 may modify the effects of greenness on SAB.