Hypothyroidism (hypothyroidism) is a group of syndromes in which the function of various body systems is reduced due to insufficient synthesis, secretion or biological effect of thyroid hormone (TH) caused by various reasons. It can be divided into three types according to the age of onset: cretinism (also known as cretinism) if it starts in the embryonic or neonatal period; juvenile hypothyroidism if it starts in childhood; and adult hypothyroidism if it starts in adults. The severity of the disease varies greatly: it can be subclinical hypothyroidism with no obvious clinical symptoms, or it can be more severe mucinous edema, or even mucinous edema coma (myxedema coma). The incidence of subclinical hypothyroidism is 3.5:1000 in women and 0.6:1000 in men per year, and the incidence of hypothyroidism is about 1:4000 to 1:3000 in newborns, and increases with age in adulthood. The incidence of subclinical hypothyroidism in the population can range from 20 per 1,000 to 120 per 1,000. The ratio of male to female hypothyroidism incidence is 1:2 to 8.