In pregnant patients, HCG secretion increases significantly in early pregnancy, so TSH levels are decreasing in early pregnancy, reaching the lowest value around 10-12 weeks of gestation, with a decrease of 30%-50% of the trough value and a median TSH of about 0.8; later TSH values gradually rebound, reaching the high limit around 33 weeks; TSH levels increase before delivery. Because of this characteristic of TSH during pregnancy, we believe that we should not use the TSH range of the general population to measure TSH levels during pregnancy; if we use the criteria of the general population, it may lead to misdiagnosis and underdiagnosis. We should have normal ranges of TSH that are specifically applicable to pregnant women, and the TSH ranges should be different for different gestational weeks. In pregnant women, treatment should be given if subclinical hypothyroidism is diagnosed, and it is recommended to control it below 2.5 mIU/L in the first trimester because in early pregnancy, the fetal thyroid gland is not yet developed, and all the thyroid hormones needed for fetal growth and development come from the mother. This period is a critical period for the development of the fetal brain and nervous system, so it is necessary to ensure an adequate supply of thyroid hormones from the mother, otherwise it will affect the intellectual development of the fetus and lower the IQ; in the second six months, it is recommended to control it below 3.5, because at this time the fetus can secrete some thyroid hormones by itself. However, it should not be oversupplemented. If the TSH is too low after maternal treatment, resulting in hyperthyroidism, it will instead increase the rate of preterm delivery and miscarriage. Therefore, the treatment target for pregnant patients is set at 0.5 mIU/L-2.5 mIU/L (especially in the first 3 months of pregnancy).