Currently, the main drugs used to treat hyperthyroidism in pregnancy include propylthiouracil (PTU) and methimazole (MMI). Both classes of drugs have teratogenic risks and the lowest effective dose should be chosen according to the patient’s condition to reduce the teratogenic risk.
Since the teratogenic risk of propylthiouracil is lower than that of methimazole, propylthiouracil is usually chosen in early pregnancy (1 to 3 months), the teratogenic sensitive period. Since PTU can cause liver damage and even acute liver failure, it is recommended to use it only in early pregnancy and liver function should be checked regularly during its use; methimazole is chosen in mid-trimester (4 to 6 months) and late pregnancy (7 to 9 months).