High thyroxine in pregnancy may be physiological and will not affect the fetus. However, hyperthyroidism cannot be ruled out. If a pregnant woman is diagnosed with hyperthyroidism, it may lead to fetal mental retardation, malformations, miscarriage and preterm delivery. 1. Physiological factors: During pregnancy, various endocrine glands are in an active state, and the thyroid gland will also undergo changes. If other functions are normal, and only T3 or T4 is mildly high, it is a normal physiological phenomenon and will not affect the fetus. 2. Hyperthyroidism: If the thyroid hormone is obviously high, accompanied by other indicators of abnormality, it may be that the pregnant woman suffers from hyperthyroidism, which will affect the normal development of the fetus, resulting in fetal mental retardation, malformation, miscarriage, preterm labor and so on. Thyroid hormone is an important indicator to check the function of the thyroid gland, which plays an extremely important role in the growth and development of the fetus. Therefore, if a pregnant woman finds her thyroid hormone level on the high side, she is advised to consult a doctor in time, and under the doctor’s guidance, improve the relevant examinations to clarify the cause and take corresponding measures.