The 'Y sign' as a novel qualitative marker for prenatal detection of aortic coarctation: a retrospective cohort study.

BACKGROUND: Prenatal diagnosis of coarctation of the aorta (CoA) remains challenging due to the high false-positive rate of traditional echocardiographic markers. This study aimed to assess the diagnostic value of a novel sonographic marker, the "Y sign," defined as the confluence of the aortic and ductal arches on the sagittal view, in predicting postnatal CoA. In addition, we evaluated the reproducibility and detectability of the "Y sign" in a large cohort of structurally normal fetuses. METHODS: A retrospective review was conducted of 9,000 fetal echocardiograms performed between January 2020 and June 2025 at a tertiary perinatology center. Fetuses with isolated suspicion of CoA were included if the aortic isthmus diameter measured in the sagittal arch view was at least 2.5 SD below the gestational age-adjusted normative mean. The presence or absence of the "Y sign," representing the branching morphology of the aortic and ductal arches, was assessed using dynamic sagittal cine imaging. Interobserver agreement for the 'Y sign' was assessed by two blinded maternal-fetal medicine specialists reviewing 200 normal fetuses (18-24 weeks), using Cohen's kappa. RESULTS: Ten fetuses met the inclusion criteria. The "Y sign" was absent in 8 fetuses, 7 of whom were postnatally confirmed to have CoA, yielding a sensitivity of 100%, specificity of 67%, and positive predictive value of 87.5%. The "Y sign" was clearly visualized in 2 fetuses, both without postnatal CoA. Among the 7 CoA-confirmed cases, bicuspid aortic valve was present in 5 (71.4%). In one "Y-negative" fetus without postnatal CoA, a shelf-like protrusion in the descending aorta was noted, though it lacked hemodynamic significance. Of 200 healthy fetuses, the 'Y sign' was concordantly positive in 169 and negative in 18 cases; 13 were discordant. Interobserver agreement was substantial (κ = 0.76), supporting reproducibility. CONCLUSIONS: The absence of the "Y sign" appears to be a sensitive and reproducible marker for prenatal CoA prediction. Although its specificity is moderate, the "Y sign" offers a practical, qualitative alternative to complex angle-based measurements, and may serve as a valuable adjunct in prenatal screening protocols, particularly when integrated with other structural and biometric parameters.