The causes of high free thyroxine T4 during pregnancy include transient hyperthyroidism of pregnancy, toxic diffuse goiter, etc. It is recommended to eliminate the disease through general treatment and medication. 1. Transient hyperthyroidism of pregnancy: this is mainly due to excessive secretion of human chorionic gonadotropin by the placenta, which leads to stimulation of the thyroid gland, resulting in high free thyroxine T4. No specific treatment is usually required for this disorder, and in most pregnant women the human chorionic gonadotropin level will gradually return to normal in the middle of pregnancy and the adverse symptoms will be relieved. If the condition is more severe, it can be treated with antithyroid drugs as prescribed by the doctor. It should be noted that the dosage of the drug must be properly controlled to avoid affecting the development of the fetus. 2. Toxic diffuse goiter: when the thyrotropic receptor produces antibodies, it will bind to the hormone receptor, which will stimulate the thyroid gland to secrete hormones, showing high T4 levels. In general, if the free thyroxine T4 level is high and accompanied by an uncomfortable reaction, it should be taken seriously and treated with anti-thyroid medication. High free thyroxine T4 during pregnancy is a common problem, so don’t panic too much, seek medical attention as soon as possible and follow your healthcare provider’s recommendations for treatment and care.