Thyroid hormones are important for the form, growth and development of the embryo and fetus. Hypothyroidism during pregnancy can lead to embryonic arrest, malformations and various growth and developmental abnormalities, and also to an increased risk of maternal complications during pregnancy. Therefore, hypothyroidism in pregnancy should be actively prevented and treated. The prevention and treatment of hypothyroidism in pregnancy includes both prevention and treatment. (1) Patients with various pre-existing thyroid diseases should have their thyroid function tested before conception, rather than after conception, to clarify their thyroid function status. If you have hypothyroidism, you should use temporary contraception and wait until the hypothyroidism is corrected before conceiving. (2) Women with hypothyroidism should be treated with levothyroxine sodium or have their levothyroxine sodium dose adjusted to bring their serum TSH level to < 2.5 mIU/L before conception. (2) Treatment: (1) The treatment goal for hypothyroidism in pregnancy is serum TSH level < 2.5mIU/L in early pregnancy and < 3.0mIU/L in mid and late pregnancy. (2) Choice of medication for hypothyroidism in pregnancy: levothyroxine sodium is preferred. (3) The requirement of levothyroxine sodium in pregnancy is related to the level of serum TSH, the higher the TSH level the higher the requirement. (4) The dose of levothyroxine sodium in pregnancy should be adjusted in a one-step method as long as the patient's condition allows, so that the patient's serum TSH level reaches the standard as soon as possible. (5) Monitoring of hypothyroidism during pregnancy, early frequency, 4 weeks, and more than in the middle and late stages. (6) Adjustment of levothyroxine sodium dose after delivery. In conclusion, ensuring normal thyroid function during the whole pregnancy is the core of hypothyroidism prevention and treatment during pregnancy. Only in this way can the risk of hypothyroidism in pregnancy be minimized.