Differences in body mass index based on self‐reported versus measured data from women veterans

OBJECTIVE: The objective was to compare differences in body mass index (BMI) calculated with self‐reported versus clinically measured pre‐conception data from women veterans in California. METHODS: Veterans Health Administration (VHA) and California state birth certificate data were used to develop a cohort of women who gave birth from 2007–2012 and had VHA data available to calculate BMI (N = 1,326 mothers, 1,473 births). Weighted Kappa statistics assessed concordance between self‐reported and measured BMI. A linear mixed‐effects model with maximum likelihood estimation, adjusted for mother as a random effect, assessed correlates of differences in BMI. RESULTS: Mean BMI was in the overweight range based on self‐reported (26.2 kg/m(2), SD: 5.2) and measured (26.8 kg/m(2), SD: 5.2) data. Weighted Kappa statistics indicated good agreement between self‐reported and measured BMI (0.73, 95% CI: 0.70, 0.76). Compared to the normal weight group, groups with overweight or obesity were significantly more likely to have lower BMIs when calculated using self‐reported versus measured heights and weights, in unadjusted and adjusted models. The finding was pronounced for class 3 obesity, which was associated with a BMI underestimation of 6.4 kg/m(2). CONCLUSIONS: Epidemiologic research that guides the clinical care of pregnant women should account for potential under‐estimation of BMI in heavier women, and perform direct measurement where feasible.