During pregnancy, low thyroid function in pregnant women can lead to adverse effects on fetal height and intelligence. Thyroxine is particularly important for fetal growth and development, and is responsible for fetal neurological and skeletal development. If thyroxine is lacking, poor neurological development can cause mental retardation; poor skeletal development can cause short and small, and severe hypothyroidism can lead to cretinism in newborns. The thyroid gland of the fetus in early and middle pregnancy cannot work yet, and the thyroxine needed depends on the mother’s supply. If the pregnant woman has low thyroid function and cannot meet the needs of the baby, she must supplement with exogenous thyroxine, which is also known as eugenol. The medication needs to be taken under the medical advice of an outpatient endocrinologist. While taking the medication, the thyroid function indicators need to be reviewed regularly every month, and the dosage of the medication should be adjusted according to the results.