Three-dimensional Evaluation of Atrioventricular Valve Geometry in the Fetal Heart: Establishing Reference Standards and Clinical Validation

Objective: To establish the reference values for the angle between the atrioventricular (AV) valve insertion levels in fetal hearts using three-dimensional ultrasound with Spatio-temporal Image Correlation (STIC) rendering and to validate these values in fetuses with confirmed congenital heart disease (CHD). Materials and Methods: A retrospective cross-sectional study was conducted using 59 STIC volumes from structurally normal fetuses between 20 and 33 + 6 weeks of gestation. The AV valve insertion angle was measured in the rendering mode of four-chamber view. A polynomial regression model was used to generate a reference curve and percentile table. A validation cohort of 26 fetuses with CHD was analyzed, and angle distributions were compared with the normative percentiles. Results: The insertion angle remained stable throughout gestation. Reference percentiles (5 th , 10 th , 50 th , 90 th , and 95 th ) were established by gestational week. Among fetuses with CHD, 46.2% had angles below the 5 th percentile and 57.7% above the 95 th percentile, with only 7.7% within the normal range. Specific CHD such as tetralogy of Fallot, transposition of the great arteries, and truncus arteriosus showed consistent deviations from normal values. Conclusion: The AV valve insertion angle was a stable parameter throughout gestation and demonstrates significant deviation in fetuses with CHD. This measurement may serve as a useful screening tool for early prenatal identification of certain structural CHD.