Abstract: Background：Severe ebstein's anomaly (EA) is challenging to diagnose using prenatal and neonatal echocardiography and generally has a poor prognosis. Although surgical treatments are gradually advancing, the short-term and long-term mortality rates for severe EA cases remain high. Objective：To explore the specific echocardiographic characteristics of misdiagnosed fetal cases of severe EA and improve the prenatal diagnosis accuracy. Design：Case series reports. Methods：Consecutive cases diagnosed with severe EA through fetal or postnatal echocardiography were retrospectively collected from May 2017 to April 2024 in two centers. We retrieved data on the mothers including age, gestational age at prenatal ultrasound, mode of conception, singleton or multiple pregnancies, medication history during pregnancy, and family history and fetuses including heart position, atrial and ventricular proportions, attachment points of the tricuspid valve leaflets, presence of tricuspid valve leaflets, papillary muscles, and chordae tendineae, development of the right ventricular outflow tract, pulmonary artery development, degree of tricuspid regurgitation, direction of ductus arteriosus blood flow, presence of other cardiac anomalies, termination of pregnancy, and surgical treatment. Main outcome measures：Echocardiographic features. Results：We enrolled 8 cases diagnosed with severe EA in the antenatal period, 7 with induction of labor, and 1 with delivery. Among the 8 cases, 1 case had ventricular septal defect (VSD) and 1 case had partial atrioventricular septal defect (AVSD). Seven cases had a complete absence and severe underdevelopment of the septal leaflet of the tricuspid valve. Among these, 2 cases also had a complete absence and severe underdevelopment of the posterior leaflet, and one case only had the posterior leaflet completely absent and severely underdeveloped. Specific prenatal echocardiographic features include paradoxical movement of the ventricular septum observed throughout the cardiac cycle; absence of chordae tendineae and papillary muscles on the right ventricular side of the interventricular septum, and a smooth right ventricular surface without soft tissue coverage, termed the "bare sign"; continuity loss of the tricuspid septal leaflet and the coronary sinus wall when the septal leaflet is absent; possible underdeveloped pulmonary artery, but normal one if VSD is present; and to-and-fro flow in the right ventricle without clear tricuspid regurgitation by Color Doppler. Conclusion：The paradoxical movement of the ventricular septum, the "bare sign" of the right ventricular surface, the tricuspid septum and the coronary sinus wall continuity loss have high specificity in the diagnosis of severe EA. Severe EA requires differential diagnosis from congenitally upguarded tricuspid valve orifice (CUTVO).

Key words: Ebstein's anomaly, Congenitally upguarded tricuspid valve orifice, Echocardiography, Fetal, Misdiagnosis