Ultrasonic estimation of fetal weight: a new predictive model incorporating femur length for the low-birth-weight fetus.

Ultrasonic measurements of biparietal diameter, head circumference, abdominal circumference, and femur length were made in 50 preterm fetuses within 48 h of delivery. Measurements of femur length in addition to fetal head and abdomen significantly improved fetal weight prediction. A computer-derived formula incorporating femur length as an index of total fetal length was derived. This predicted 84% of weights within 10% of the birth weight. Comparisons with other formulas are given.