Comparison of 2- and 3-Dimensional Sonography for Estimation of Birth Weight and Neonatal Adiposity in the Setting of Suspected Fetal Macrosomia

OBJECTIVES To compare the accuracy of 2-dimensional (2D) and 3-dimensional (3D) fetal measurements for prediction of birth weight Z score and neonatal adiposity (percent body fat) in the setting of suspected fetal macrosomia. METHODS We conducted a prospective observational study of term singleton pregnancies with suspected macrosomia. Patients were enrolled on admission to labor and delivery and underwent sonographic examinations. Within 48 hours of delivery, neonatal anthropometric measurements were obtained. RESULTS Thirty-four neonates were included in the analysis. Mothers were very obese (mean body mass index ± SD, 39.1 ± 7.8 kg/m(2)); 56.5% were white; and 39.1% had diabetes. Neonates were 38% female and had a mean birth weight of 3940.0 ± 496.8 g, percent body fat of 18.5% ± 4.0%, and Ponderal index of 2.8 ± 0.3 g/cm(3). Mean 2D estimated fetal weight was 3973 ± 443 g; mean 3D estimated fetal weight was 3803 ± 528 g; and mean thigh volume was 102.5 ± 19.6 cm(3). Both 2D and 3D measurements accounted for about half the variance in predicted birth weight (R(2) for 2D = 0.53, 71% within 10% of birth weight; R(2) for 3D = 0.47, 65% within 10% of birth weight). Thigh volume Z score was the prenatal parameter most highly correlated with both birth weight Z score (R(2) = 0.52; r = 0.72; 95% confidence interval, 0.54-0.84; P < .001) and percent body fat (R(2) = 0.22; r = 0.47; 95% confidence interval, 0.17-0.69; P = .04). CONCLUSIONS In our population of fetuses with suspected macrosomia, fractional thigh volume was the best sonographic estimate of neonatal percent body fat and birth weight Z score. Future research on prediction of neonatal weight and adiposity in macrosomic fetuses should include an estimate of fetal soft tissue given the generalized increase in body fat of these fetuses.