Introduction: Thyrotoxicosis in pregnancy presents the challenge of maintaining a normal level of maternal free thyroid hormone, while minimizing adverse drug effects, obstetric complications, and the risk fetal hypothyroidism. Propylthiouracil is used for treatment in the first trimester with thyroidectomy typically performed in the second trimester if PTU/ MTZ are intolerable or if thyrotoxicosis persists. When thyroidectomy is indicated, thyroid hormone levels must be normalized prior to the operation, as there is risk of thyroid storm that can occur during and up to several hours postoperatively. In such cases, preoperative plasmapheresis may be considered. Case Presentation: We present a 24 year old G2P0101 Hispanic female who reported to the ED with throat pain, chills, tachycardia, and shortness of breath who was found to have a TSH less than 0.005, free T4 3.15, elevated alkaline phosphatase, and an incidentally discovered early pregnancy approximately 4 - 6 weeks gestation. Medical history includes hyperthyroidism with over ten hospitalizations for thyrotoxicosis within the last three years and preterm delivery during her first pregnancy. A recent thyroid biopsy in 2017 showed a benign multinodular goiter. She had been taking methimazole and current CT of the neck demonstrated marked thyroid goiter with mild tracheal narrowing and mild tonsillitis. She was discharged on propylthiouracil 100 mg TID, metoprolol 25 mg TID, and augmentin 875 mg BID with the goal of decreasing her free T4 and T3 in preparation for thyroidectomy. Four days later, the patient returned to the ED with similar symptoms. Labs revealed TSH 0.001, free T4 3.70, FreeT3 15.1 WBC 3.1, platelets 103, and elevated total bilirubin, transaminases, and alkaline phosphatase. EKG demonstrated sinus tachycardia with minimal diffuse ST depression. Ultrasound showed a 0.34 cm round hypoechoic focus in the endometrial cavity without a fetal pole or cardiac activity. Chest X-ray demonstrated minor bibasilar atelectasis. The patient was admitted and PTU was discontinued due to leukopenia and elevated transaminases. Dexamethasone was started and metoprolol was continued. Total thyroidectomy was planned for when free T4 less 2.0 The patient received two treatments of plasmapheresis, which decreased free T4 to 2.11 and then to 1.40. The thrombocytopenia and transaminitis resolved A total thyroidectomy was performed and well tolerated. patient had full term pregnancy, uneventful delivery while on thyroid hormone replacement. Conclusion : Preoperative plasmapheresis can be considered for the normalization of free T4 if thionamides fail or cannot be tolerated. This case demonstrates the successful management of thyrotoxicosis with plasmapheresis in the first trimester of pregnancy.to Our knowledge Plasmapheresis was not used before in Pregnancy in preparation for thyroidectomy.

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