Thyroid hormones have an important influence on the entire process of fetal brain development. In early pregnancy, the mother provides all the thyroid hormones required by the fetus. In mid-pregnancy, the fetal thyroid gland gradually matures, but most of the fetal thyroid hormones are still provided by the mother. In late pregnancy, fetal thyroid hormone requirements are mainly synthesized by the fetus itself, and only 10% is provided by the mother. Hypothyroidism in pregnancy is recognized to cause neurointellectual impairment in the offspring, and many studies have shown that maternal subclinical hypothyroidism can reduce mental and motor scores in the offspring.