Background Despite accumulating evidence linking greenness with the decreased risk of low birthweight (LBW), the potential modification and mediation effects of ambient air pollution remain unstudied. Methods We conducted a nationwide birth cohort analysis using nearly 3.9 million registry-based mother-infant records across 31 provinces in Iran during 2013–2018. Greenness exposure during pregnancy was assessed utilizing the normalized difference vegetation index (NDVI) within multiple buffers (500–3000 m). Logistic regression model was used to analyze the associations of maternal greenness exposure with LBW and small for gestational age (SGA). Modification effects of PM2.5 and O3 levels were checked via comparing greenness-related risks in stratified analyses by grouping maternal air pollution exposure into low, medium, and high levels based on cut-points at tertiles. Mediation analysis was adopted to quantify the degree to which PM2.5 and O3 exposure mediated the associations of greenness exposure with LBW and SGA. Results We observed consistently lower LBW and SGA risks in relation to greater greenness within buffers of 500–3000 m. Each 0.1-unit rise of NDVI within the 3000-m buffer (NDVI-3000 m) was associated with an estimated odds of 0.902 (95% confidence interval [CI]: 0.900–0.905) for LBW and 0.887 (95% CI: 0.886–0.889) for SGA. Stratified analyses provided consistent evidence for greater greenness-related protective effects in lowering LBW and SGA risks at higher PM2.5 and O3 levels in multiple age subgroups. Among the entire group with maternal age of 15–49 years, for instance, LBW risk for each 0.1-unit rise in NDVI-3000 m declined by 6.8% (95% CI: 6.4%–7.2%), 10.1% (95% CI: 9.7%–10.6%), and 10.9% (95% CI: 10.4%–11.3%) in the 1st to 3rd tertile stratum of PM2.5 levels, respectively. The mediation analysis suggested a significant mediating role of ambient air pollution in greenness-LBW/SGA association, where reduced PM2.5 and O3 mediated 2.2%–3.4% and 7.3%–12.1% risks during the pregnancy. Conclusions This study provided national evidence for greater health benefits of greenness in alleviating LBW and SGA risks among pregnant women being exposed to higher PM2.5 and O3 pollution levels. Reduced PM2.5 and O3 may partially mediate the association of greenspace exposure with fetal growth.

Prenatal greenness exposure and the decreased risk of low birthweight and small for gestational age: modification and mediation effects of air pollution

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2025年11月18日

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Dinghua Zhan,
Boning Deng,
Yixiang Wang,
Yaqi Wang,
Qiang Li,
Fatemeh Mayvaneh,
Yunquan Zhang

摘要

Background

Despite accumulating evidence linking greenness with the decreased risk of low birthweight (LBW), the potential modification and mediation effects of ambient air pollution remain unstudied.

Methods

We conducted a nationwide birth cohort analysis using nearly 3.9 million registry-based mother-infant records across 31 provinces in Iran during 2013–2018. Greenness exposure during pregnancy was assessed utilizing the normalized difference vegetation index (NDVI) within multiple buffers (500–3000 m). Logistic regression model was used to analyze the associations of maternal greenness exposure with LBW and small for gestational age (SGA). Modification effects of PM_2.5 and O₃ levels were checked via comparing greenness-related risks in stratified analyses by grouping maternal air pollution exposure into low, medium, and high levels based on cut-points at tertiles. Mediation analysis was adopted to quantify the degree to which PM_2.5 and O₃ exposure mediated the associations of greenness exposure with LBW and SGA.

Results

We observed consistently lower LBW and SGA risks in relation to greater greenness within buffers of 500–3000 m. Each 0.1-unit rise of NDVI within the 3000-m buffer (NDVI-_3000 m) was associated with an estimated odds of 0.902 (95% confidence interval [CI]: 0.900–0.905) for LBW and 0.887 (95% CI: 0.886–0.889) for SGA. Stratified analyses provided consistent evidence for greater greenness-related protective effects in lowering LBW and SGA risks at higher PM_2.5 and O₃ levels in multiple age subgroups. Among the entire group with maternal age of 15–49 years, for instance, LBW risk for each 0.1-unit rise in NDVI-_3000 m declined by 6.8% (95% CI: 6.4%–7.2%), 10.1% (95% CI: 9.7%–10.6%), and 10.9% (95% CI: 10.4%–11.3%) in the 1st to 3rd tertile stratum of PM_2.5 levels, respectively. The mediation analysis suggested a significant mediating role of ambient air pollution in greenness-LBW/SGA association, where reduced PM_2.5 and O₃ mediated 2.2%–3.4% and 7.3%–12.1% risks during the pregnancy.

Conclusions

This study provided national evidence for greater health benefits of greenness in alleviating LBW and SGA risks among pregnant women being exposed to higher PM_2.5 and O₃ pollution levels. Reduced PM_2.5 and O₃ may partially mediate the association of greenspace exposure with fetal growth.