Reference Range of Fetal Renal Volume by Three-Dimensional Ultrasonography Using the Vocal Method

Abstract

Objective: To establish reference values for fetal renal volume by three-dimensional sonography using the VOCAL (Virtual Organ Computer-Aided Analysis) method. Methods: This prospective longitudinal study involved 57 healthy pregnant women who were examined between 24 and 34 weeks of pregnancy. Each fetal kidney was evaluated separately using the VOCAL method with a 30° rotation angle. For each gestational age, the following measures were obtained for the right and left kidneys: mean, standard deviation, minimum and maximum values, and the 5th, 10th, 25th, 50th, 75th and 90th percentiles. Polynomial regression models were constructed to assess the relationship between renal volume and gestational age, adjusted by the determination coefficient (R²). The Wilcoxon test was used to evaluate the concordance between the right and left renal volumes. Bland-Altman graphs were used to assess intra- and inter-observer variability. Results: The right renal volume increased from 4.5 ± 1.3 cm³ at 24 weeks to 12.1 ± 1.5 cm³ at 34 weeks. The left renal volume increased from 4.6 ± 0.8 cm³ at 24 weeks to 11.9 ± 1.1 cm³ at 34 weeks. There was a strong correlation between both the right and left renal volumes and gestational age (R² = 0.975 and 0.970, respectively). There were no significant differences between the right and left renal volumes. The mean difference between repeated measures by the same examiner was –0.07 cm³ (–0.88 to 0.75) for the right kidney and –0.21 cm³ (–0.95 to 0.75) for the left kidney. The mean difference between repeated measures obtained by two different examiners was –0.07 cm³ (–1.25 to 1.12) for the right kidney and 0 cm³ (–1.53 to 1.53) for the left kidney. Conclusion: Reference values were generated for fetal renal volume assessed by three-dimensional ultrasonography using the VOCAL method.