Comparison of estimated fetal weights using volume and 2-dimensional sonography and their relationship to neonatal markers of fat.

OBJECTIVE: The purpose of this study was to compare the accuracy of traditional 2-dimensional sonographically estimated fetal weight (EW2D) with 3-dimensional volume-based estimated fetal weight (EW3D) and to evaluate the relationship between fetal limb volume, birth weight, and markers of neonatal adiposity. METHODS: Fifty singleton pregnancies at 32 to 42 weeks' gestation underwent sonographic evaluation within 48 hours of delivery. We compared the accuracy of the EW2D and EW3D in the prediction of birth weight. The Ponderal index, sum of all skin fold measurements, estimated neonatal fat mass, and percent body fat were calculated. Paired t tests, simple regression analyses, a chi(2) test, and the Steiger z test were used where appropriate. P< .05 was considered significant. RESULTS: The mean birth weight+/-SD was 3130+/-589 g at 38.8+/-2.1 weeks. The EW2D (r(2)=0.66) and EW3D (r(2)=0.76) estimates were both correlated with birth weight. The birth weight and neonatal fat mass were more highly correlated with the sonographically based thigh volume (r(2)=0.67 and 0.61) than femur length (r(2)=0.41 and 0.37). The mean percent error between EW2D and birth weight was larger (-3.3%+/-11.6%) than the mean percent error of EW3D (0.7%+/-9.2%; P= .0004). CONCLUSIONS: Sonographically based fetal limb volumes, especially the fractional thigh volume, reflect neonatal fat mass and are better correlated with birth weight.