Concordance between self-reported pre-pregnancy body mass index (BMI) and BMI measured at the first prenatal study contact

Abstract

Background: The 2009 Institute of Medicine (IOM) gestational weight recommendations are tailored to women’s pre-pregnancy body mass index (BMI). Limited evidence exists on methods for estimating women’s pre-pregnancy BMI, particularly for women living in low and middle income countries. Using data from collected among Peruvian pregnant women, we compared the concordance between self-reported pre-pregnancy BMI with BMI measured at the earliest prenatal study visit. Methods: Data were from the Pregnancy Outcomes Maternal and Infant Study (PrOMIS), a cohort of pregnant women at the Instituto Nacional Materno Perinatal (INMP) in Lima, Peru. 2605 women aged 18 to 49 years (mean ± SD gestational age = 10.9 ± 3.3 weeks) were included in the study. Self-reported pre-pregnancy weight and height and measured weight and height were collected at the first prenatal study contact. We assessed the concordance between measured and self-reported BMI; and, the agreement among indicators of nutritional status obtained using measured and self-reported BMI. Results: On average, weight measured at the first prenatal study visit was 0.27 kg higher than self-reported pre-pregnancy weight (p < 0.05); and, measured height was 0.02 m lower than self-reported pre-pregnancy height (p < 0.001). Correspondingly, measured BMI was 0.71 kg/m2 higher than self-reported BMI (p < 0.001). Scatter and Bland-Altman plots indicated strong concordance between measured and self-reported BMI. The proportion of women in the normal BMI category tended to be higher when using self-reported BMI (59.6 %) than when using measured BMI (50.4 %). Conversely, the proportion of women in the overweight or obese BMI categories tended to be lower when using self-reported BMI (38.2 %) than when using measured BMI (47.7 %). Conclusion: Self-reported pre-pregnancy BMI was strongly correlated with BMI measured at the first prenatal study contact. The findings potentially suggest that, in this context, there is minimal change between pre-pregnancy BMI and BMI measured at the first prenatal study contact; or, that women in this study just recalled their most recent measured anthropometrics (including values obtained during the index pregnancy but before enrollment in the PrOMIS study). Electronic supplementary material The online version of this article (doi:10.1186/s12884-016-0983-z) contains supplementary material, which is available to authorized users.