Body mass index: a true indicator of body fat in obese gravidas

OBJECTIVE: To determine the relationship between body mass index (BMI) and percent body fat in overweight/obese pregnant women (BMI >25) before and during pregnancy. STUDY DESIGN: Thirteen overweight women were evaluated longitudinally (prospective cohort study design) before conception, in early gestation (12-22 weeks) and in late gestation (31-36 weeks). BMI was calculated as weight (kg)/height (m)2, and percent body fat was estimated using hydrodensitometry with correction for residual lung volume. RESULTS: The correlation between BMI and percent body fat before conception was r2 = 0.86 (p = 0.001). Furthermore, the correlation remained strong in early pregnancy, r2 = 0.84 (p = 0.001), but was less strong yet significant, r2 = 0.54 (p = 0.004), in late gestation. CONCLUSION: In overweight women, the correlation between BMI and percent body fat remained significant during pregnancy. However, the correlation weakened as the pregnancy advanced.