Waist-to-Hip Ratio versus Body Mass Index as Predictor of Obesity-Related Pregnancy Outcomes

Objective In nonpregnant populations the waist-to-hip ratio (WHR) is a better predictor of obesity-related outcomes than body mass index (BMI). Our objective was to determine, in pregnancy, the relationship between these measures of obesity, and large-for-gestational age (LGA) and cesarean delivery (CD). Methods This is a secondary analysis of data from the Combined Antioxidant and Preeclampsia Prediction Study. Women with a WHR of ≥ 0.85 and 0.80 to 0.84 at 9 to 16 weeks gestation were compared with those with a WHR < 0.80. Women with early pregnancy BMI ≥ 30.0 kg/m² (obese) and 25.0 to 29.9 kg/m² (overweight) were compared with those < 25.0 kg/m². LGA was defined as > 90% by Alexander nomogram. Univariable analysis, logistic regression, and receiver operating characteristic curves were used. Results Data from 2,276 women were analyzed. After correcting for potential confounders, only BMI ≥ 30 was significantly associated with LGA (adjusted odds ratio [aOR]: 2.07, 1.35-3.16) while BMI 25.0-29.9 (aOR: 1.5, 0.98-2.28), WHR 0.8-0.84 (aOR: 1.33, 0.83-2.13), and WHR ≥ 0.85 (aOR: 1.05, 0.67-1.65) were not. Risk for CD was increased for women with elevated WHR and with higher BMI compared with normal. Conclusion WHR is not associated with LGA. While BMI performed better than WHR, neither was a strong predictor of LGA or need for CD in low-risk nulliparous women.