Early First-Trimester Diagnosis of Thoracopagus Conjoined Twins with a Shared Cardiac Structure.

Thoracopagus conjoined twins are the most common type of conjoined twinning and are frequently associated with shared cardiac anatomy, the principal determinant of prognosis and postnatal survival. Early prenatal diagnosis is essential for accurate counseling and timely pregnancy management. We report the diagnosis of thoracopagus conjoined twins with a shared cardiac structure in a 35-year-old primigravid woman at 8 weeks and 3 days of gestation. High-resolution transvaginal ultrasound demonstrated persistent thoracic fusion, fixed relative fetal position, a single yolk sac, a single umbilical cord, and absence of an intertwin membrane. Color Doppler confirmed a single sonographically detectable cardiac complex, while three-dimensional ultrasound enhanced spatial visualization and facilitated parental counseling. Differential diagnoses, including monochorionic twins with close apposition, TRAP sequence, body stalk anomaly, and other forms of conjoined twinning, were systematically excluded. Early first-trimester recognition of thoracopagus conjoined twins with shared cardiac anatomy is feasible using dynamic ultrasound and Doppler imaging. Establishing the diagnosis before the end of the first trimester enables accurate prognostic assessment, timely multidisciplinary counseling, and informed parental decision-making for this condition associated with an extremely poor prognosis.