The main treatment for hypothyroidism is thyroid hormone replacement therapy to maintain normal thyroid function, which generally requires lifelong treatment. The drug of choice for the treatment of hypothyroidism is levothyroxine. The dose of drug replacement is related to the patient’s age and weight, and the treatment dose should be individualized. Maintenance doses for adults tend to be in the range of 50-200ug/day. The half-life of levothyroxine is 7 days, and about 80% is absorbed after oral administration. The equilibrium of blood concentration can be reached about 6 weeks after taking the drug. The indicators for reaching maintenance dose are improvement of clinical symptoms, normalization of T3, T4 and TSH. Pregnant women should control TSH below 2.5mU/L and FT4 at the high end of the normal range level. The active ingredient of levothyroxine is thyroid hormone, which is a normal hormonal component of the human body and has no teratogenic effect and will not adversely affect pregnant women and fetuses, so it can be safely administered. It should be noted that some hormones secreted by the placenta during pregnancy will affect the metabolism of thyroid hormones, which is one of the reasons for hyperthyroidism during pregnancy. Therefore, the treatment of hypothyroidism during pregnancy requires special attention to dose adjustment, which should be adjusted to normal levels as soon as possible, and regular monitoring of hormone levels and timely dose adjustment. For some patients with severe hypothyroidism and serious complications such as hypothyroid heart disease and mucinous edema coma, or female patients whose hypothyroidism cannot be effectively controlled, pregnancy should not be carried out and should be terminated if necessary. Therefore, the treatment of hypothyroidism during pregnancy still mainly relies on levothyroxine therapy, but regular testing of hormone levels and timely adjustment are needed. Most patients’ conditions can be controlled for safe pregnancy, but some of those with serious complications or whose conditions cannot be controlled should consider termination of pregnancy.