Comparison of greenness measures in assessing the association between urban residential greenness and birth weight

With a cohort of 138,532 births in metropolitan Atlanta, Georgia, 2000-2002, this study compared four types of greenness measures, along with multiple buffer distances around maternal residences, in assessing the association between maternal exposure to residential greenness and birth weight. In addition to the widely-used average of normalized difference vegetation index, percent tree canopy, and proximity to parks, our study innovatively included the neighborhood green index that considered both the abundance and quality of greenness. We also investigated the potential distance decay effect of surrounding greenness on birth weight. The un-adjusted models showed that all greenness measures were significantly associated with birth weight and the risk of low birth weight. However, after adjusting for a comprehensive list of individual and neighborhood characteristics, all associations were attenuated, and higher birth weights were only significantly associated with higher measures of the neighborhood green index at all buffer distances and the absence of parks within 800 m of the mother's home. No significant relationships were found between any greenness measures and the risk of low birth weight. In addition, some evidence was seen that immediate surrounding greenness had a greater protective effect on birth weight than remote greenness. Also, the highest SES group presented stronger associations between greenness and birth weight than other SES groups. Our study suggests the need to take greenness quality into account when assessing the impact of greenness exposure on public health and developing health-related policies.