Anthropometric estimation of maternal body composition in late gestation

Objective: To construct a model to estimate maternal body composition in la te gestation using anthropometric measurements. Methods: Twenty healthy pregnant women at 30 weeks' gestation had estimates of body composition using hydrodensitometry, with corrections for residual lung volume, and total body water using H-2 O-18 (development group). Tota l body water was estimated from O-18 abundances measured by gas-isotope-rat io mass spectrometry. Maternal age, height, weight, and seven skinfold site s were correlated with fat mass using stepwise regression analysis. The ant hropometric model to estimate fat mass was then tested prospectively in a s econd group of 20 subjects and correlated with underwater weighing and tota l body water measurements (validation group). Statistical analysis used chi (2), paired t and Wilcoxon sign-rank tests. Results: There were no statistically significant differences in maternal de mographics between groups. The fat mass of development group subjects using underwater weighing and total body water was 22.7 +/- 7.6 kg. Using the de velopment group, a model was derived that explained 91% of the variance in fat mass by underwater weighing and total body water using maternal weight and triceps, subscapular, and suprailiac skinfolds (r(2) = 0.91, P <.001). When tested prospectively in the validation group, the correlation remained statistically significant (r(2) = 0.89, P <.001). There was no statistical ly significant (P =.88) difference between the anthropometric estimates of fat mass and underwater weighing and total body water measurements (95% con fidence interval -2.476, 2.748 kg of fat mass). Conclusion: This anthropometric model can be used to predict maternal fat m ass in late gestation. (Obstet Gynecol 2000;96:33-7. (C) 2000 by The Americ an College of Obstetricians and Gynecologists.).