Accuracy of Current Body Mass Index Obesity Classification for White, Black, and Hispanic Reproductive-Age Women

OBJECTIVE: To compare the National Institutes of Health's (NIH) body mass index (BMI)-based classification to identify obesity in comparison with the World Health Organization (WHO), which uses percent body fat, among white, black, and Hispanic reproductive-aged women. METHODS: Body weight, height, BMI, and percent body fat (dual-energy X-ray absorptiometry generated) were determined for 555 healthy adult women aged 20-33 years (mean +/- standard deviation 26.5 +/- 4.0 years). Diagnostic accuracy of the NIH-based obesity definition (BMI of 30 kg/m(2) or higher) was determined using the WHO criterion standard (percent body fat greater than 35%). RESULTS: Obesity as defined by the NIH (BMI 30 kg/m(2) or higher) and by WHO (percent body fat greater than 35%) classified 205 (36.9%) and 350 (63.1%) of the women as obese, respectively. The NIH-defined obesity cutoff values had 47.8%, 75.0%, and 53.9% sensitivity in white, black and Hispanic, women, respectively. White and Hispanic women had 2.9% greater percent body fat than black women for a given BMI. Receiver operating characteristics curves analyses showed that the respective sensitivities improved to 85.6%, 81.3%, and 83.2%, and that 311 women (56.0%) were classified as obese as a whole when race or ethnic-specific BMI cutoff values driven by our data (BMI at or above 25.5, 28.7, and 26.2 kg/m(2) for white, black, and Hispanic women, respectively) were used to detect percent body fat-defined obesity. CONCLUSION: Current BMI cutoff values recommended by the NIH failed to identify nearly half of reproductive-aged women who met the criteria for obesity by percent body fat. Using race or ethnic-specific BMI cutoff values would more accurately identify obesity in this population than the existing classification system. (Obstet Gynecol 2010;115:982-8)