Maternal altitude and risk of low birthweight: A systematic review and meta-analyses

Previous studies conducted in high altitude regions showed that maternal altitude was associated with low birth weight. The effect size of birth weight reduction is inclusive with unknown effects due to preterm birth. We systematically reviewed the literature and synthesize evidence on associations between altitude elevation from sea level and birth weight.

We searched MEDLINE/PubMed, Embase, Scopus, Web of Science, and Cochrane database, from inception to May 5, 2020 for studies that reported maternal altitude and birth weight. Bayesian multilevel effect models were employed to estimate the effect size on birth weight (and gestational age) associated with altitude. Bayesian multilevel effect models were employed to estimate the effect size on birth weight (and gestational age) associated with altitude.

The systematic search identified 1020 articles, with 52 articles meeting the inclusion criteria providing 207 estimates for the association of altitude and birth weight (n = 4,428,563), and with 22 articles providing 71 estimates for gestational age (n = 2,149,627). A reduction in mean birth weight of 96.98 g was associated with every 1000 m increase in altitude across 52 studies. A statistically significant but numerically minimal effect of maternal altitude elevation was observed on the gestational age (0.3 days), corresponding to a negligible estimation of 5 g lower birth weight. A relatively high heterogeneity of between-study association (I²>84.1%) and small study effect was found.

A clinically meaningful birth weight reduction was associated with maternal altitude elevation beginning from sea level. Future longitudinal studies are needed to elucidate the causal association and to understand the late effect of maternal altitude.