Patients with hypothyroidism can take oral levothyroxine sodium (L-T4) under the guidance of the doctor to reduce thyroid stimulating hormone (TSH) to below 2.5 mIU/L before pregnancy. The treatment of hypothyroidism is mainly to supplement the lack of thyroid hormone, clinically preferred levothyroxine, hypothyroidism patients after pregnancy for the demand for thyroid hormone will also change with the weeks of pregnancy, usually after pregnancy L-T4 replacement dose should be increased than the pre-pregnancy by 30% to 50%, and need to monitor the thyroid function on a regular basis. Hypothyroidism is harmful to women of childbearing age. If treatment is not timely, it may cause infertility and increase the risk of miscarriage, preterm labor and other adverse pregnancy outcomes; poorly controlled hypothyroidism during pregnancy may lead to mental retardation and short stature in newborns. Patients with hypothyroidism should go to the endocrine clinic before pregnancy to confirm whether the thyroid function is controlled in the normal range and whether it is suitable for pregnancy, and should keep a close eye on the changes in thyroid function after pregnancy in order to avoid adverse outcomes.