SUN-357 Hydatidiform molar pregnancy with co-existing live fetus complicated by thyrotoxicosis

Abstract Disclosure: R. Wang: None. S.S. Kim: None. N. Mirsaidi: None. A.W. Wang: None. C. Taneja: None. Background: A complete hydatidiform mole with a coexisting live fetus is a rare event associated with obstetric complications including vaginal bleeding, preeclampsia, and hyperthyroidism. We discuss a patient who developed thyrotoxicosis during her first trimester due to presence of a hydatidiform mole with a coexisting live fetus. Case Presentation: Here we present a 36-year-old G3P1011 female at 14-weeks' gestation who was referred to the endocrinology clinic for new onset hyperthyroidism. The patient’s prior fetal ultrasound showed an abnormal avascular area with an adjacent fetus and placenta. These findings were concerning for hydatidiform complete mole with coexisting live fetus. Initial laboratory evaluation showed TSH <0.01 uIU/mL, FT4 3.6 ng/dL, and hCG 603,833 mIU/mL. At the time of presentation, the patient reported severe nausea/vomiting, tremors, and palpitations. Patient was started on methimazole (later transitioned to PTU) and beta blockade and was planned for dilation and curettage (D&C). Approximately one week later, the patient presented to the emergency room for vaginal bleeding and was admitted to the OB service. At the time of presentation, TSH remained undetectable with FT4 of 3.3 ng/dL, TT3 372 ng/DL, and hCG was >1,000,000 mIU/mL. The patient was continued on thionamide and beta blocker therapy and urgently underwent D&C. After the procedure, thyroid and hCG levels were serially monitored and eventually normalized. Surgical pathology confirmed presence of a complete molar pregnancy with twin fetus. Conclusion: Hydatidiform moles with a live fetus are particularly challenging cases due to the medical risks associated to the mother and fetus. Hyperthyroidism is a common complication that can be difficult to treat with medical management alone, which often leaves dilation and evacuation as the sole treatment option. This case highlights the importance of managing such patients with a multidisciplinary approach, with collaboration from endocrinology, obstetrics and anesthesia teams. Presentation: Sunday, July 13, 2025