About 90% of congenital hypothyroidism is due to impaired thyroid development, with twice the incidence in girls than boys, and in 1/3 of cases the thyroid gland is completely absent. The thyroid gland may be underdeveloped during the intrauterine stage, or it may remain in any part of the body between the subungual and the normal position of the thyroid gland during the downward migration, forming an ectopic thyroid gland, which is normally located in the anterior inferior part of the cervical thyroid cartilage. Most of these hypoplastic thyroid glands are partially or completely deprived of their secretory function, and most children are born with a deficiency of thyroid hormones, while only a few may develop deficiency symptoms as late as several years after birth. The cause of this thyroid insufficiency has not yet been elucidated and may be related to genetic qualities and immune-mediated mechanisms. 2. Defects in the thyroxine synthesis pathway: The second most common cause of congenital hypothyroidism. This defect can occur in any of the processes of thyroid hormone synthesis and is mostly an autosomal recessive disorder. 3.Thyroid hormone deficiency: Hypothyroidism caused by pituitary gland secretion of thyroid stimulating hormone disorder is common in idiopathic hypopituitarism or hypothalamus and pituitary gland developmental defects, among which thyroid stimulating hormone release hormone deficiency is more common. 4, iodine deficiency endemic hypothyroidism: due to the lack of iodine in the diet of pregnant women, resulting in the fetus in the embryonic period due to iodine deficiency, resulting in hypothyroidism, although this situation is rare in China, but in individual areas can still be seen. 5. Transient hypothyroidism in newborns: This is caused by the entry of thyrotropin receptor blocking antibodies into the fetus through the placenta, which usually disappears within 3 months.