The different reference values of thyroid function in different stages of pregnancy are the key to diagnose hyperthyroidism in pregnancy. 1) TSH: In the first half of normal pregnancy, blood please TS is lower than the reference range of non-pregnancy, therefore, a lower serum TSH value with normal FT4 level in early pregnancy does not indicate that thyroid function is abnormal, while the lower limit of TSH in non-pregnancy population can be referred to in the second half of pregnancy. 2) FT3 and FT4: Serum FT3 and FT4 rise in the early stages of pregnancy. As pregnancy progresses, FT3 and FT4 levels gradually decrease, and in the second half of pregnancy, the reference values are 10_30% lower than the non-pregnant reference values. For patients diagnosed with hyperthyroidism early in pregnancy, treatment with propylthiouracil (PTU) is initiated, while TRAb levels are tested, and if elevated, they are retested at 22-26 weeks of gestation. For patients diagnosed with hyperthyroidism after midtrimester, treatment with methimazole (MMI) should be initiated and TRAhb levels should be checked and retested at 22-26 weeks of gestation if elevated. If thyroidectomy is chosen, midtrimester is the best time.