The Association of Neighborhood Socioeconomic Status with Birth Weight is Not Confounded by Ambient Air Pollution in Twin Pregnancies: A Retrospective Cohort Study.

Abstract

Introduction: This study examines the association of neighborhood socioeconomic status (SES) with birth weight and gestational age in a population-based twin cohort, adjusting for ambient PM₁₀ and NO₂ exposure. By accounting for placentation, we aim to disentangle the independent and combined effects of socioeconomic and environmental factors.

Methods: Neighborhood SES was defined using maternal residence at birth and statistical sectors (average area: 1.55 km2) to define annual median neighborhood household income. PM₁₀ and NO₂ exposure was estimated using a spatial-temporal interpolation method (Kriging) integrating daily monitoring data and land cover data. Analyses were stratified by placentation: one placental mass or two separate placentas. Multivariable linear mixed models were conducted for birth weight as outcome, linear regression models for gestational age.

Results: For twins with two separate placentas, per EUR 3,000 (∼1 SD) increase in median neighborhood household income, birth weight increased with 46.83 grams. Adjustment for PM₁₀ and NO₂ did not change the associations. A part of these associations was explained by gestational age, as the association was reduced to 21.92 grams per EUR 3,000 increase. Each EUR 3,000 increase in annual median neighborhood household income corresponded to a longer gestation of 26 h, independent of ambient air pollution or other covariates.

Discussion: Although neighborhood SES and ambient air pollution are correlated with birth outcomes, they act through different paths in this twin cohort. This approach provides insights into the etiology of adverse birth outcomes in a high-risk population, even in high-income settings with universal healthcare access.