When hypothyroidism occurs during pregnancy, it is generally appropriate to control thyroid hormone (TSH) below 2.5 mIU/L. The goal of TSH control can be raised after 30 weeks of pregnancy to within 3.0 mIU/L. For pregnant women with hypothyroidism, early miscarriage, fetal death, malformation, growth restriction, and congenital defects may occur for the fetus. For pregnant women, they may have placental abruption, heart failure and other problems. Therefore, in case of hypothyroidism in pregnant women, replacement therapy with levothyroxine sodium is recommended, and TSH levels are checked regularly. In the process of control, it is also necessary to pay attention to the levels of free T3, free T4, anti-thyroid peroxidase antibodies and anti-thyroglobulin antibodies. Pregnant women should not stop using thyroid hormone or reduce the dosage of thyroid hormone without permission, as this may lead to recurrence of hypothyroidism in pregnant women, causing thyroid stimulating hormone levels to rise again and exceed the ideal target value for control, which may lead to some hindrance of fetal growth and development. In addition, it is recommended that pregnant women have regular health checkups and pay close attention to their body changes and thyroid function to ensure the normal development of the fetus.