The thyroid gland of the fetus is not yet formed in early pregnancy, and the thyroid hormones needed for fetal growth and development are supplied by the mother through the placenta. Therefore, thyroid hormone deficiency in early pregnancy not only affects the growth and development of the fetus, but also has an impact on the development of the fetal nervous system. Therefore, when hypothyroidism is detected in early pregnancy, the following should be done: 1. Give levothyroxine sodium tablets for replacement therapy as soon as possible, and the starting dose should be as large as possible to normalize the thyroid function in the shortest possible time. 2. Review thyroid function regularly during pregnancy and adjust the dose of medication to keep TSH less than 2.5mU/L throughout pregnancy. 3. The patient should not stop the medication without permission.4. Undergo regular prenatal checkups to detect possible fetal malformations and various dysplasias as early as possible.