Abstract
Fetal mediastinal teratomas are rare tumors that can lead to serious complications such as fetal hydrops and intrauterine fetal death. Early prenatal diagnosis is critical in patient counseling, management, and preparation for postnatal interventions. In this report, we present the case of a 27-year-old woman in the second trimester of a dichorionic diamniotic twin pregnancy, in which the presenting fetus was diagnosed with a mediastinal teratoma and subsequently developed fetal hydrops, leading to intrauterine death. The diagnosis was initially made via ultrasound and the second twin exhibited no major anomalies. Following the fetal demise of the affected twin, a cesarean section was performed due to suspected maternal complications, and the surviving twin was delivered prematurely. This case highlights the importance of multidisciplinary collaboration in the management of complex twin pregnancies and underscores the challenges of diagnosing and managing rare fetal anomalies.