Nomogram of fetal upper arm volume by three-dimensional ultrasound using extended imaging virtual organ computer-aided analysis (XI VOCAL).

Aim: To define the reference range of the fetal upper arm volume by three-dimensional (3D) ultrasound using the eXtended Imaging Virtual Organ Computer-aided AnaLysis (XI VOCAL) method.

Methods: This prospective, cross-sectional study enrolled 425 healthy pregnant women with 20-40 weeks of gestation. The XI VOCAL technique was used for the volumetric calculations, considering 10 sequential sectional plane areas, performed along the axial plan of the fetal upper arm. The proximal and distal epiphyses were the beginning and final reference. Second degree polynomial regression models were created to evaluate the correlation between the volume of the fetal arm and the gestational age (GA), determining the 5th, 10th, 25th, 50th, 75th, 90th and 95th corresponding percentiles. The intraclass correlation coefficient (ICC) was used to evaluate the intra- and interobserver reproducibility.

Results: The mean fetal upper arm volume ranged from 4.59-1.18 (3.10-7.40 cm(3)) to 53.87-10.72 cm(3) (40.30-76.60 cm(3)). The fetal upper arm volume and GA were highly associated (R(2)=0.913). The intra- and interobserver reproducibility were reliable, with ICC=0.997 (95% CI 0.995-0.999) and 0.996 (95% CI 0.993-0.998), respectively.

Conclusion: The reference range for the fetal upper arm volume was determined by 3D-ultrasound using the XI VOCAL method, and was found to be highly reproducible.