The number of endocrine clinics is huge, and more than half of the patients have recently been seen for thyroid-related disorders. In recent years, the impact of thyroid function on pregnancy and the postpartum period is receiving more and more attention, and the number of patients consulted and treated for thyroid disorders in pregnancy, especially hypothyroidism in pregnancy, is increasing. This article summarizes the treatment of hypothyroidism in pregnancy with reference to the latest guidelines and clinical experience. Thyroid function in pregnancy Thyroid stimulating hormone (TSH) is the most accurate indicator of the functional status of the thyroid gland during pregnancy. If the laboratory cannot establish a normal range of TSH values specific to each trimester, the following reference values are recommended: 0.1-2.5 mIU/L in the first trimester; 0.2-3.0 mIU/L in the middle trimester; and 0.3-3.0 mIU/L in the second trimester. Hypothyroidism in pregnancy Excluding secondary factors such as pituitary TSH tumors and thyroid hormone resistance syndrome, hypothyroidism in pregnancy can be a significant problem. (1) Clinical hypothyroidism with elevated TSH levels >2.5 mIU/L and reduced FT4 concentrations. If the TSH level is 10.0 mIU/L or higher, clinical hypothyroidism should be considered regardless of whether the FT4 level is lower than normal. (2) Subclinical hypothyroidism Serum TSH is between 2.5 and 10 mIU/L, but FT4 concentration is normal. (3) Maternal isolated hypotension Maternal TSH level is normal, but FT4 concentration is below the 5th or 10th percentile of the normal reference value for pregnancy. Clinical experience (1) All clinical hypothyroidism during pregnancy should be treated For women planning to become pregnant, TSH should be controlled to below 2.5 mIU/L before pregnancy. Lower levels of TSH before pregnancy (within the normal reference range for non-pregnant women) may reduce the likelihood of increased TSH in the first trimester of pregnancy. In patients with hypothyroidism on LT4 therapy, further clarification of pregnancy is required in the event of menopause or a positive home pregnancy test, and a 25%-30% increase in LT4 dose is required in women with definite pregnancy. (2) No treatment is needed for isolated maternal low T4 in pregnancy. To date, no studies have confirmed the benefit of treating isolated maternal low T4 and therefore routine FT4 screening in pregnant women is not recommended. （The need for LT4 therapy in pregnant women with subclinical hypothyroidism is not well documented, regardless of whether the TPOAb is normal or not. The goal of LT4 therapy is to restore the serum TSH value to the normal level in pregnancy, taking into account the adverse effects of subclinical hypothyroidism.