Fetal thigh volume by 3D sonography using XI VOCAL: Reproducibility and reference range for BRAian healthy fetuses between 20 and 40weeks

Objective: To provide reference values for fetal thigh volume using three-dimensional (3D) ultrasound and the eXtended Imaging Virtual Organ Computer-aided AnaLysis (XI VOCAL) method. Methods: This is a cross-sectional study that enrolled 425 healthy pregnant women between the 20 ^th and 40 ^th weeks of gestation. The XI VOCAL was performed along the axial cross-section in ten sequential areas for the volumetric calculations, having the proximal and distal echogenic diaphysis as references. Second-degree polynomial regression models, with the determination of percentiles, were created to evaluate the relation between the fetal thigh volume and gestational age (GA). Intraoperator and interoperator reproducibility was evaluated using intraclass correlation coefficient. Results: The mean fetal thigh volume varied from 8.00 (3.90-11.90cm ³) to 122.14cm ³ (105.0-153.50cm ³) at 20 and 40weeks of gestation, respectively. Fetal thigh volume was strongly correlated with gestational age, and the reference values can be obtained by the following mathematical equation: fetal thigh volume (cm ³)=68.70-7.63×GA+0.23×GA ² (R ²=0.946). The intraoperator and interoperator reproducibility were excellent, with an intraclass correlation coefficient=1.000 and 0.999, respectively. Conclusions: The reference range of fetal thigh volume was determined by 3D-ultrasound using the XI VOCAL method.