The effect of area-level average income and individual level factors on small-for-gestational age: a population-based study of the Vancouver census metropolitan area, 2006-2009

The goal of this paper was to identify area- and individual-level predictors of small for gestational age birth (SGA). This cross-sectional study analyzed live singleton births from 2006 to 2009 in the Vancouver Census Metropolitan Area. Hierarchical logistic regression models were used to model odds of SGA with deprivation. A crude model of area-level average income was compared to models adjusted by individual-level variables. A strong association was found between SGA and material deprivation, which was greatly influenced by area-level average income. Individual-level variables attenuated the association between area-level average income and odds of SGA. Maternal race/ethnicity was found to have the strongest effect in reducing the area-level association with SGA. No association was found between area-level average income and SGA except in the White group. Future research should attempt to determine if maternal race/ethnicity variable stands as a proxy for structural, biological, social, behaviour/lifestyle, and/or environmental factors.