<prompt> DOC for hyperthyroidism in pregnancy:PropylthiouracilMethimazoleI-131Thyroxine  <response>: Ans. a PropylthiouracilRef DC Dutta 7th ed. 287; Harrisons 19th ed. 2297 For the hyperthyroidism during pregnancy the mainstay of treatment in 1st trimester is PTU or methimazole. Methimazole is preferable avoided during first trimester of pregnancy if PTU is available. Methimazole and carbimazole is avoided due to fetal aplasia cutis and other defects such as choanal atresia. Because of its rare association with hepatotoxicity, propylthiouracil should be limited to the first trimester and then maternal therapy should be converted to methimazole or carbimazole. 