Critical window of gestational greenspace exposure for the risk of low birth weight.

Many studies link average residential greenspace exposure during pregnancy to birthweight changes, but evidence on critical timing for low birthweight is limited. Furthermore, coarse aggregations of exposure levels throughout pregnancy may obscure complex exposure-response relationships. This case-control study using the birth data (n = 788,275) in three US states examined the associations between the ZIP code-level weekly enhanced vegetation index (EVI) levels during gestational weeks 0-39 and term low birthweight (TLBW). The logistic regression with distributed lag non-linear functions, adjusted for maternal characteristics and season, estimated odds ratios (OR) of TLBW per interquartile range increase (0.200) in weekly EVI. Week-specific ORs showed an inverted U-shape. Significant ORs were observed in weeks 0-7 and 30-39, ranging from 0.989 (95% CI: 0.978-0.999) to 0.996 (95% CI: 0.992-1.000). Results highlight the importance of higher greenspace exposure in early and late pregnancy for reducing TLBW risk, informing policy and future research.