The diagnosis of hypothyroidism during pregnancy is different from that of non-pregnant women due to the influence of hormones secreted by the placenta and changes in immune function. At the same time, the treatment of hypothyroidism in pregnancy has attracted enough attention because of the obvious effects of thyroid function on both the fetus and the mother. However, how to treat it and whether to treat it are still the main reasons why the majority of patients are confused. Zhang Jiping, Department of Endocrinology, The First People’s Hospital of Lianyungang City Hypothyroidism in pregnancy is divided into three types: clinical hypothyroidism, subclinical hypothyroidism, and hypothyroxinemia. The following is a brief description of each. First, clinical hypothyroidism is characterized by decreased thyroid hormones (decreased FT3 and FT4) and increased thyrotropin (increased TSH). Since maternal thyroid hormone is an important hormone for fetal neurological development in early pregnancy, maternal thyroid hormone deficiency can lead to fetal brain development disorders and mental retardation after birth, therefore, clinical hypothyroidism should be treated actively, especially in early pregnancy, and the earlier the treatment, the better. Secondly, subclinical hypothyroidism, i.e., normal thyroid hormones (FT3, FT4) and elevated thyrotropin (TSH). However, there are two different types of this condition. Mothers who are thyroid peroxidase positive (TPOAb positive) should be treated aggressively. For TPOAb-negative mothers, due to the lack of sufficiently convincing clinical studies, or even inconsistent results of clinical studies, the treatment of TPOAb-negative subclinical hypothyroidism is neither recommended nor opposed at home and abroad, but it is recommended to review the condition regularly, monitor it every 4 weeks, and treat it promptly if it develops into clinical hypothyroidism. Third, hypothyroxinemia, in which thyrotropin is normal (normal TSH) but thyroid hormone is decreased (decreased FT4). In this condition, most cases occur due to inadequate iodine intake during pregnancy, and the benefits and drawbacks of treatment may be equal, so current guidelines do not routinely recommend treatment, and regular review is recommended. In cases of persistent and progressive decreases, personal experience suggests that treatment should be given. In addition, it is common in our clinic to see normal thyroid hormones and thyrotropin (normal FT3 and FT4, normal TSH) but elevated thyroid peroxidase (elevated TPOAb). Since residual thyroid hormones in the first 3 months of pregnancy are able to fulfill the needs of pregnancy, there is no significant effect on early fetal neurologic development, and all guidelines generally do not recommend treatment. However, TPOAb is involved in the destruction of thyroid tissue, and subclinical hypothyroidism and clinical hypothyroidism may occur in the middle and late stages of pregnancy; therefore, regular monitoring is required, and treatment is given promptly when TSH elevation occurs. Personal clinical experience suggests that since current clinical studies indicate that TPOAb positivity increases the risk of miscarriage and preterm labor, patients with a past history of preterm labor and miscarriage should be treated.