Twin Pregnancy With Discordant Pathology: A Case of Molar Gestation and Viable Co-twin After Assisted Conception.

Complete hydatidiform mole with a coexisting viable twin is an exceptionally rare condition. It poses significant maternal risks, including hemorrhage, early-onset preeclampsia, and progression to gestational trophoblastic neoplasia. The use of assisted reproductive technology (ART) has increased the detection of such complex gestations, yet optimal management remains controversial. We present the case of a 23-year-old primigravida who conceived a dichorionic diamniotic twin pregnancy following frozen embryo transfer. Early ultrasound demonstrated one normally developing gestational sac with a viable fetus and a second irregular, avascular sac with cystic degeneration. Serum β-human chorionic gonadotropin (β-hCG) levels were markedly elevated for gestational age. Over the following weeks, the abnormal sac exhibited progressive molar changes, accompanied by recurrent vaginal bleeding and a persistent subchorionic hematoma. The viable co-twin continued to grow appropriately. Given the escalating maternal risk, multidisciplinary counseling was undertaken, and the patient elected to terminate the pregnancy. Suction evacuation was performed without complication. Histopathological examination confirmed hydatidiform mole. Post-evacuation β-hCG levels declined rapidly, and the patient remained well on serial follow-up. This case illustrates the diagnostic and management challenges of a complete hydatidiform mole with a coexisting viable twin in an ART pregnancy. Early diagnosis, close surveillance, and multidisciplinary counseling are critical for balancing maternal safety with fetal viability in these high-risk gestations.