Clinical hypothyroidism in pregnancy definitely requires treatment, and oral levothyroxine (LT4) therapy is recommended; to avoid TSH elevation in early pregnancy, LT4-treated hypothyroid women are required to maintain their TSH concentration at a level of less than 2.5 mIU/L until they are ready to become pregnant; clinical hypothyroidism requires an increase in the dose of eugenol of about 30% per day after pregnancy because of the increased thyroid hormone requirement after pregnancy that The dose of eugenol needs to be increased by about 30% per day after pregnancy because of the increased need for thyroid hormones after pregnancy, until it reaches steady-state at 20 weeks of gestation. In TPOAb-positive subclinical hypothyroidism, L-T4 therapy is recommended. The treatment of subclinical hypothyroidism in pregnancy is the same as for clinical hypothyroidism, with the same goals and frequency of monitoring. Specific serum TSH therapeutic targets: 0.1~2.5 mIU/L in T1 stage (early pregnancy, i.e., the first 3 months), 0.2~3.0 mIU/L in T2 stage of mid-pregnancy, and 0.3~3.0 mIU/L in T3 stage of late pregnancy; once clinical hypothyroidism is identified, treatment should be immediately initiated to achieve the above therapeutic targets as early as possible. Frequency of monitoring: The frequency of thyroid function monitoring in pregnant women with clinical hypothyroidism during the first half of pregnancy (1-20 weeks) is 1 time/4 weeks. Depending on the degree of TSH elevation, different doses of L-T4 are given. When TSH is above the upper limit of the pregnancy-specific reference value, the starting dose of L-T4 is 50 μg/d; when TSH is above 8.0 mIU/L, the starting dose is 75 μg/d; and when TSH is above 10 mIU/L, the starting dose is 100 μg/d. The dose can be adjusted according to the therapeutic goal of TSH. For pregnant women with subclinical hypothyroidism and TPOAb-negative TPOAb, the guidelines do not recommend or oppose LT4 therapy; for pregnant women with simple hypo-T4emia (TPOAb-negative TPOAb), the guidelines do not recommend routine use of LT4. Selenium preparation is not recommended for pregnant women with TPOAb-positive TPOAb. Oral levothyroxine (LT4) to maintain normal maternal thyroid function does not interfere with breastfeeding. Clinically hypothyroid pregnant women can have their LT4 dose reduced to pre-pregnancy levels after delivery and have their serum TSH levels rechecked at 6 weeks postpartum to adjust the LT4 dose. Newborns are usually screened for TSH in plantar blood 48 hours to 7 days after birth, and if it is greater than 10-20 mIU/L, venous blood TSH, TT4, and FT4 need to be checked, and serum TSH is greater than 9 mIU/L and FT4 is less than 7.7 pmol/L as a reference for newborns with congenital hypothyroidism. Hyperthyroidism in pregnancy Patients with hyperthyroidism should, in principle, get pregnant after their hyperthyroidism improves and stop taking medication; if they are unable to stop taking medication, they can consider taking medication to get pregnant. Hyperthyroidism in pregnancy PTU (propylthiouracil) is recommended for T1 (early pregnancy, i.e., the first 3 months), methimazole is recommended for T2 and T3 (middle and late pregnancy), and the combination of antithyroid drugs (ATDs) and LT4 is not recommended, except for the treatment of rare fetal hyperthyroidism. Blood counts, liver function, and thyroid function need to be monitored every 4 weeks to adjust drug dosage, and usually antithyroid medications need to be tapered in late pregnancy. Non-iodized salt is not recommended during pregnancy. Beta-blockers are not recommended in pregnancy because prolonged use of propranolol (cardiac glycosides) in pregnant women can cause intrauterine growth retardation, fetal bradycardia, and neonatal hypoglycemia; If a pregnant woman has active hyperthyroidism or a past history of hyperthyroidism, the concentration of thyroid hormone receptor antibody (TRAb) must be measured in the pregnant woman at 20 to 24 weeks of gestation; In patients with toxic diffuse goiter who need to breastfeed, use a dose of antithyroid medication that is not recommended. For patients with toxic diffuse goiter (Graves’ disease) who need to breastfeed, moderate doses of ATDs are safe (e.g., propylthiouracil <300 mg/d or methimazole <20-30 mg/d); ATDs should be given in divided doses immediately after breastfeeding, but the infant's thyroid function should be monitored.