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

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.

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.

Mean BMI was in the overweight range based on self-reported (26.2 kg/m², SD: 5.2) and measured (26.8 kg/m², 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/m².

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.