Hypothyroidism in pregnancy refers to hypothyroidism that occurs during pregnancy, i.e., a condition in which the thyroid gland is unable to synthesize or secrete enough thyroxine to meet the body’s needs. Early pregnancy, i.e. the first 12 weeks of pregnancy, is the first rapid development period of fetal brain development, but at this time, the thyroid function of the fetus itself has not yet been established, 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 has been able to synthesize thyroid hormone, but the amount is relatively small, and still need to rely on the mother’s hormone to help. If the mother suffers from hypothyroidism in early pregnancy, it will affect the brain development of the fetus, and even cause irreversible damage, resulting in a 6-8 point drop in the IQ of the offspring. Therefore, early detection of hypothyroidism in pregnancy is crucial. Women should be highly alert to the possibility of hypothyroidism in pregnancy if they experience the following symptoms: fatigue, drowsiness, fear of cold, memory loss, weight gain, depression, constipation, menstrual disorders, joint or muscle pain, thinning and brittle hair or nails, etc. Mild hypothyroidism has no or only mild symptoms. Mild hypothyroidism with no or only mild clinical symptoms can be easily confused with pregnancy reactions and is not easily diagnosed. You can also use the hypothyroidism in pregnancy self-measurement chart for self-measurement. If there are five or more yeses, please go to the endocrinology department of a regular hospital for a blood index test of the five items of the thyroid function. Early diagnosis, early treatment, and supplementation of adequate amount of exogenous thyroxine (e.g. oral levothyroxine sodium tablets) throughout the pregnancy and breastfeeding period can effectively prevent the decline of fetal intelligence level.