Tricuspid valve (TV) abnormalities, including Ebstein's anomaly and TV dysplasia, are rare congenital heart deseases (< 1% of CHD). Tricuspid regurgitation (TR) often worsens in the second trimester due to increased fetal cardiac output and right heart dominance and postnatal prognosis remains challenging. The Isthmic Systolic Index (ISI), reflecting right- and left-heart contributions in the aortic isthmus, may indicate disease progression. ISI was derived from the ratio Ns (Systolic Nadir)/PSV (Peak Systolic Velocity). In severe TR, reduced right ventricular output lowers the systolic nadir, leading to increased ISI as TR severity advances.

To demonstrate a difference in the ISI between fetuses with TV abnormalities associated with poor prognosis versus those with a more favorable outcome.

This multicenter retrospective study in Québec, Canada (13 years) includes all fetuses with TV abnormalities, excluding those with major CHD, extracardiac malformations, or any fetal conditions affecting isthmic flow. Fetal echocardiography, maternal records, and postnatal outcomes will be reviewed to assess prognostic factors for TV disease severity. Severe or poor prognosis will be defined in utero by hydrops, intrauterine death, or medical termination of pregnancy, and postnatally by neonatal death, univentricular physiology, or subsequent mortality.

Approximately 60 patients will be included across three centers, with 1–3 echocardiograms analyzed per patient. To date, 44 patients have been included in the main center, with 44% classified as severe. Comparison of ISI between severe and non-severe groups shows a significant increase in ISI in the severe group. We expect to confirm these results by including patients from two additional centers, and we aim to determine a predictive cut-off for poor prognosis using ISI according to gestational age.

TV abdnormalities are rare fetal heart defects with often severe outcomes, including intrauterine death or univentricular physiology postnatally. Traditional prognostic factors have not considered aortic isthmus Doppler. We propose a novel approach by analyzing fetal hemodynamics to assess postnatal outcomes and better guide prenatal counseling.