Fetal weight prediction by thigh volume measurement with three-dimensional ultrasonography.

OBJECTIVE: To evaluate the usefulness and accuracy of a simple method of predicting fetal weight by measuring fetal thigh volume with three-dimensional ultrasonography.

METHODS: In 84 pregnant women, fetuses without structural or chromosomal anomalies were studied prospectively and cross-sectionally. Biparietal diameter (BPD), abdominal circumference (AC), and femur length (FL) were measured by two-dimensional ultrasound. Fetal thigh volume was measured by three-dimensional ultrasound, using three cross-sectional images of femur, from proximal, middle, and distal parts of femur diaphysis. Infants were delivered within 48 hours after ultrasound examinations.

RESULTS: Modified thigh volume measurements using three cross-sectional images of femur by three-dimensional ultrasound were correlated strongly with birth weight (R(2) = 0.921, P <.001). Using linear and polynomial regression, we calculated a new best-fit formula: Birth weight (g) = 165.32 + 28.78 x modified thigh volume (mL). The mean and standard deviation of the residual were 121.8 and 110.4, respectively, in three-dimensional formulas, which were significantly smaller than those of two-dimensional formulas.

CONCLUSION: Thigh volume measurement using three cross-sectional images of femur by three-dimensional ultrasound was simple, and there was better accuracy with this method than with two-dimensional ultrasound methods for predicting fetal weight during the third trimester of pregnancy.