Racial/Ethnic Disparities in Inadequate Gestational Weight Gain Differ by Pre-pregnancy Weight

Pre-pregnancy body mass index (BMI) varies by race/ethnicity and modifies the association between gestational weight gain (GWG) and adverse pregnancy outcomes, which disproportionately affect racial/ethnic minorities. Yet studies investigating whether racial/ethnic disparities in GWG vary by pre-pregnancy BMI are inconsistent, and none studied nationally representative populations. Using categorical measures of GWG adequacy based on Institute of Medicine recommendations, we investigated whether associations between race/ethnicity and GWG adequacy were modified by pre-pregnancy BMI [underweight (<18.5 kg/m(2)), normal weight (18.5-24.9 kg/m(2)), overweight (25.0-29.9 kg/m(2)), or obese (≥30.0 kg/m(2))] among all births to Black, Hispanic, and White mothers in the 1979 USA National Longitudinal Survey of Youth cohort (n = 6,849 pregnancies; range 1-10). We used generalized estimating equations, adjusted for marital status, parity, smoking during pregnancy, gestational age, and multiple measures of socioeconomic position. Effect measure modification between race/ethnicity and pre-pregnancy BMI was significant for inadequate GWG (Wald test p value = 0.08). Normal weight Black [risk ratio (RR) 1.34, 95 % confidence interval (CI) 1.18, 1.52] and Hispanic women (RR 1.33, 95 % CI 1.15, 1.54) and underweight Black women (RR 1.38, 95 % CI 1.07, 1.79) experienced an increased risk of inadequate GWG compared to Whites. Differences in risk of inadequate GWG between minority women, compared to White women, were not significant among overweight and obese women. Effect measure modification between race/ethnicity and pre-pregnancy BMI was not significant for excessive GWG. The magnitude of racial/ethnic disparities in inadequate GWG appears to vary by pre-pregnancy weight class, which should be considered when designing interventions to close racial/ethnic gaps in healthy GWG.