Validity of Self-Reported Pre-Pregnancy Weight and Body Mass Index Classification in an Integrated Health Care Delivery System

Abstract

Background: Self-reported weight prior to pregnancy is prone to error. We utilised a measured pre-conceptional weight from the electronic health record (EHR) to investigate error in recalled pre-pregnancy body mass index (BMI) category and compared how associations between pre-pregnancy BMI and pregnancy outcomes varied by using the two measures.

Methods: We assessed differences in means, correlations, and categorisation of pre-pregnancy BMI for 5092 singleton pregnancies delivered between 2007 and 2013 in Kaiser Permanente Northern California. Associations between measured and self-reported BMI category and gestational diabetes, infant size for gestational age, and exceeding the Institute of Medicine gestational weight gain recommendations were assessed.

Results: Overall, the two measures assigned the same BMI category for 86.7% of women with higher risks of misclassification for overweight (Relative Risk (RR) 3.38, 95% Confidence Interval (CI) 2.79, 4.10), obese class I (RR 3.81, 95% CI 3.07, 4.75), and obese class II (RR 1.80, 95% CI 1.28, 2.55) women compared to normal weight women. However, associations between self-reported or measured BMI category and several pregnancy outcomes were similar.

Conclusions: Despite misclassification, self-reported and measured pre-pregnancy weights were similarly associated with perinatal outcomes in this study population. Our results illustrate the value of the EHR for recording measured pre-pregnancy weight for use in research.

Keywords: BMI; Body Mass Index; Body weight; Pregnancy; Validation; Weight Variability.