Application of serum TSH in diagnosis There is no pregnancy-specific TSH reference range, the reference range of TSH in early pregnancy should be 30-50% lower than that of non-pregnant population, the reference range of TSH in normal human is 0.5-5.0mIU/L, some scholars proposed 2.5mIU/L as the upper limit of the normal range of TSH in early pregnancy. Application of serum TT4/FT4 in diagnosis There is no pregnancy-specific TT4/FT4 reference range, FT4 fluctuates widely and is influenced by the test method, which is not recommended. TT4 concentration increases steadily and is about 1.5 times higher than that in non-pregnancy, and the application of TT4 is internationally recommended to assess thyroid function in pregnancy. Treatment L-T4 is the preferred replacement therapy drug, L-T4 treatment goal and dose adjustment, hypothyroidism diagnosed before pregnancy, adjust L-T4 dose, TSH normal before pregnancy. During pregnancy, the L-T4 dose is increased by 30%-50% compared to non-pregnancy. Diagnose hypothyroidism during pregnancy and treat immediately with L-T4 2.0 μg/kg/d. Adjust the L-T4 dose according to the pregnancy-specific normal range of TSH. Some scholars suggest TSH 2.5 mIU/L as the target value for L-T4 supplementation, and measure TSH every 2-4 weeks if the L-T4 dose is adjusted. The earlier the target is reached, the better (preferably within 8 weeks of gestation). after the TSH target is reached, TSH, FT4 and TT4 should be monitored every 6-8 weeks. there is no consensus on whether to treat pregnant women with subclinical hypothyroidism. the simultaneous intake of L-T4 with ionic supplements, ion-containing multivitamins, calcium and soy foods should be avoided and should be separated by more than 4 hours. Prevention Consensus: Pre-pregnancy screening should be done for people at high risk of hypothyroidism. People at high risk of hypothyroidism include: 1. those with personal and family history of thyroid disease; 2. those with history of goiter and thyroid surgical resection and 131I treatment; 3. those previously found to have elevated serum TSH or positive thyroid autoantibodies; 4. those with personal and family history of other autoimmune diseases.