Fetal weight estimation from ultrasonic three-dimensional head and trunk reconstructions: evaluation in vitro.

The theoretical usefulness of volume as a predictor of fetal weight was assessed on 25 dead neonates with weight ranges between 364 and 3,650 gm. The correlation between volume, measured by water displacement, and weight was r = 0.999, with a standard error of 37 gm. A method is described for using volume, calculated from three-dimensional ultrasonic head and trunk reconstructions, to predict fetal weight. For the dead neonates, the correlation between measured weight and calculated head plus trunk volume was r = 0.985, with a standard error of 190 gm. The regression coefficient was 1.73, thus indicating that head and trunk volumes underestimate weight, as might be expected since limbs were not included. We conclude from this "ideal" situation that volume measurements will eventually provide the best estimates of fetal weight, and that three-dimensional head trunk reconstructions are reasonably accurate measures of overall volume.