Prepregnancy weight, socioeconomic status, and racial differences in gestational weight gain: Exploring impacts of confounding and interaction

Background: Impacts of prepregnancy body mass index (BMI) and socioeconomic status (SES) on established racial differences in gestational weight gain (GWG) have not been thoroughly studied. This study aims to investigate confounding by type of SES measure and interactions between race and prepregnancy BMI in order to better characterize racial differences in GWG. Methods: We estimated racial difference in GWG (continuous and categorical using 2009 Institute of Medicine recommendations) using data from 4516 births to black, Hispanic, and non-black, non-Hispanic (predominantly white) mothers in the1979 National Longitudinal Survey on Youth. SES was measured using percent poverty, employment, mother's education, and grandmother's education. Additional covariates included marital status, parity, smoking during pregnancy, and gestational age. Results: Strength of confounding varied by SES measure, with percent poverty accounting for most of this relationship. Adjusted interaction models showed that normal weight black women had lower mean GWG (kg) compared to normal weight non-black, non-Hispanic women (β=-1.0; CI=-1.64, -0.34). Both normal (OR=1.86; CI=1.36, 2.56) and overweight (OR=2.09; CI=1.11, 3.94) black women were more likely to gain inadequately compared to their non-black, non-Hispanic counterparts. No significant racial differences in any measure of GWG were found for Hispanic women or among obese women. Conclusion: It is important to consider SES measurement type when estimating racial differences in GWG. Additionally, these racial differences may be more relevant in normal and overweight women than obese women. These findings should be considered in future research on GWG and may also be relevant in studies aimed at normalizing prepregnancy weight.