Objective: To determine reference values for the fetal cisterna magna volume by three-dimensional ultrasonography (3DUS) using the virtual organ computer-aided analysis (VOCAL) method.
Methods: A cross-sectional study was conducted with 224 healthy pregnant women between 17 and 29 completed weeks. Measurement of the fetal cisterna magna volume was performed in the standard axial plane of the transverse diameter of the cerebellum through the VOCAL method with a 30° angle. For the determination of reference values, polynomial regressions with adjustments by the coefficient of determination (R(2)) were held. The reliability and agreement were made by the intra-class correlation coefficient (ICC) and limits of agreement of the Bland-Altman graph.
Results: The average of the fetal cisterna magna volume ranged from 0.73 ± 0.25 to 3.79 ± 1.10 cm(3) between 17 and 29 weeks, respectively. Correlation was observed between the fetal cisterna magna volume and the gestational age (GA), best represented by a quadratic equation: -1.918+0.0284 × GA + 0.0065 × GA(2) (R(2 )= 0.67). It was observed good reliability and intra-observer agreement, with ICC = 0.92 and 95% limits of agreement (-49.7; 48.4). There was low inter-observer reliability and agreement, with ICC = 0.58 and 95% limits of agreement (-114.0; 80.2).
Conclusion: Reference values for the fetal cisterna magna volume by 3DUS using the VOCAL method were determined and showed good agreement and intra-observer reliability.
Keywords: Cisterna magna; VCAL; fetus; reference range; three-dimensional ultrasound.