Birth weight is an important predictor of infant mortality and adverse events in childhood. Birth weight has become the focus of attention within the literature on the impact of the natural environment. The findings from this line of research could have important public health, community design and policy implications and it is therefore important to synthesize the evidence across studies to determine if a consensus exists. This article reports on the results of a meta-analysis of eight studies of the impact of green spaces or general greenery in the living environment of pregnant mothers on the birth weight of their babies. The eight studies reviewed were cohort studies including 214,940 participants, written in English or Spanish, published between 2011 and early 2014, and conducted in Europe, North America and Asia. Two experts conducted the review, with a third consulted in cases of reviewer disagreement, and inter-rater agreement was good.
The eight studies had generally similar methodologies and levels of quality (moderate to high) and were therefore comparable. They statistically controlled for most relevant confounding variables, with the exception of noise pollution in some studies. Seven of the eight studies reported a positive association between greenness and birth weight. The other study found this effect only for mothers in the lowest educational group. The meta-analysis across the eight studies found that neighborhood greenness within a 100 meter buffer of the mother's home was associated, though weakly, with birth weight. A smaller number of articles contributed to an analysis of the association between greenness within a 250 or 500 meter buffer (a distance requiring the mother to transport herself to the green space). Wider buffers were associated with a stronger greenness-birth weight effect, suggesting that the social function of urban green spaces, rather than the stress reduction effect of being able to see green around the home, might be responsible for the effect.
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