Reference curves of first-trimester novel measurements of the fetal urinary tract using three-dimensional ultrasound and Virtual Reality

The aim of this research was to assess the feasibility and reproducibility of first-trimester biometric and volumetric measurements of the fetal urinary tract (FUT) using three-dimensional (3D) ultrasound (US) and Virtual Reality (VR), and to establish reference curves. In a prospective cohort, 2D- and 3D-US datasets of pregnancies (gestational age (GA) 11⁺⁰-14⁺⁶ weeks) were obtained. Novel biometric and volumetric FUT measurements were performed using 3D VR and compared with 2D US measurements. Reproducibility was evaluated through intra-, interobserver and intersystem agreement (ICC, Bland-Altman). All measurements were plotted against GA to create reference curves. A total of 108 3D-US datasets (mean GA 12⁺⁶ weeks (SD 5 days) mean CRL 67 mm (SD 9.0 mm)) were selected randomly. Using 3D VR, intra- and interobserver analyses showed moderate-good agreement for all FUT measurements (ICCs >0.77) and renal calyces (ICCs 0.51-0.83). Volumetric measurements showed the highest agreement (ICC >0.96). Comparison of 2D-US and 3D VR demonstrated good agreement (ICC 0.81). Mean relative differences were <10 % for all measurements except coronal renal calyx measurements. All FUT dimensions increased with GA and reference curve were constructed. First-trimester FUT measurements using 3D VR are feasible and reproducible, except for renal calyces. These measurements provide an in-vivo description of early FUT growth with potential diagnostic value for anomalies.