Hypothyroidism in pregnancy is a condition in which a woman develops hypothyroidism during pregnancy, meaning that her body’s thyroid gland cannot synthesize or secrete enough thyroxine to meet her body’s needs. During the first 12 weeks of pregnancy, the fetal brain is developing rapidly, but the fetus has not yet established its own thyroid function, and the thyroid hormone needed for fetal brain development is completely dependent on the mother’s supply. After 3 months, the fetus’ own thyroid gland is able to synthesize thyroid hormone, but the amount is small and the mother’s hormones are needed to help. If a mother has hypothyroidism in early pregnancy, it can affect the fetal brain development and even cause irreversible damage, resulting in lower IQ in the offspring. Studies from the United States show that mothers with thyroid disorders (mostly hypothyroidism and, to a lesser extent, hyperthyroidism) produce babies with birth defects (brain, kidney and heart defects, as well as cleft lip, cleft palate and polydactyly) at a rate of about 18 percent. In contrast, the percentage of babies with birth defects in the general population is only about 3%. Therefore, it is advisable for women with hypothyroidism and other thyroid disorders to have their fetuses screened for birth defects, such as heart defects, at an early age. Hypothyroidism not only affects the next generation, but also has a significant impact on a woman’s own health. Because hypothyroidism may start with mild symptoms in the early stages, it can lead to mental depression and physical disorders, and even prevent women of childbearing age from having a normal pregnancy and childbirth. While women may enjoy the joy of being a mother for the first time, they are at a higher risk of developing postpartum thyroiditis after delivery, with about 7% of women developing abnormal thyroid function within one year after delivery. If not detected and treated in time, the risk of myocardial infarction, renal failure and even cognitive impairment in old age is greatly increased. The only way to prevent mental impairment in offspring is to screen for hypothyroidism before or early in pregnancy and treat it early, so caring for thyroid health, early diagnosis, and standardized treatment with levothyroxine is crucial for both mother and child.