[Can 3D volumetric analysis of the fetal upper arm and thigh improve conventional 2D weight estimates?]

To determine the usefulness of three-dimensional ultrasound volumetry of fetal thigh and upper arm in predicting weight at delivery.

Inclusion criteria to our prospective study were single-ton pregnancies with a planned or expected delivery within 96 hours of enrollment. In 74 patients (formula-finding group) standard fetal biometry, followed by measurement of thigh and upper arm volumes by three-dimensional ultrasound, was performed. Subsequently, our new 3D-formulas were tested in a prospective validation group of 52 patients.

Both upper arm and thigh volumes correlated well with birth weight (r2 = 0.95, respectively, p < 0.0001). The best result, however, was achieved by a combination of standard 2D-measurements with the volumetric data of upper arm and thigh (r2 = 0.98, p < 0.0001). With use of polynomial regression analysis we obtained two best-fit formulas: BIRTH WEIGHT: -263.8 +13.7269 x Arm Volume +7.16575 x Thigh Volume +148.2 x ATD. Birth weight: -1288.7 +51.9502 x Arm Volume -0.252 x Arm Volume 2 -2.1766 x Thigh Volume +0.0321 x Thigh Volume 2 +36.2509 x GA -0.7526 x GA2 +654.3 x BIP -36.6136 x BIP2 -381.8 x ATD +24.0927 x ATD2.

Three-dimensional volumetry of the fetal thigh and upper arm may improve prediction of birth weight. Further larger studies are needed to validate our results.