Measurement of limb circumferences with three-dimensional ultrasound for fetal weight estimation.

A large number of formulae have been published for fetal weight estimation. This study examines the possibility of using three-dimensional ultrasound to measure the limb circumference. This technology provides us with the opportunity to visualize two simultaneous, orthogonal planes, allowing the exact determination of the transverse plane at the mid-point of the limb. A total of 157 patients were scanned in the week prior to delivery. The following variables were measured in 154 fetuses: biparietal diameter, head circumference, transverse abdominal diameter, abdominal circumference, femur length, thigh circumference and arm circumference. The whole population was split into three subgroups according to the abdominal circumference centile (< 10th centile, 10-90th centile, and > 90th centile), because this single variable has the strongest correlation with neonatal weight (R = 0.901). With forward stepwise multiple regression analysis, four models were elaborated, one for the whole population and one for each subgroup. The small-for-dates fetuses need a targeted formula including only two variables, thigh circumference and femur length. Our data suggest that the thigh circumference measurement improves the estimation for growth-retarded fetuses and that the arm circumference improves the weight prediction for the others. The measurement of the two variables, made possible with three-dimensional ultrasound, has improved our results in fetal weight estimation.