Low thyroid stimulating hormone (TSH) during pregnancy is considered to be caused by factors such as transient thyrotoxicosis of pregnancy and diffuse toxic goiter. Doctor’s advice is needed for targeted treatment, such as regular checkups, medication, and so on. 1. Transient thyrotoxicosis of pregnancy: It is caused by high concentration of chorionic gonadotropin stimulating the TSH receptor of the thyroid gland. No special treatment is needed in this type of cases, and regular checkups are sufficient. 2. Diffuse toxic goiter (Graves’ disease): the patient’s body may produce thyroid-stimulating hormone receptor antibody (TRAb), which leads to thyroid cell hyperplasia causing increased secretion of thyroid hormone, resulting in hyperthyroidism and ultimately a decrease in TSH. Such cases should be treated with the appropriate medication according to the pregnancy. In case of low thyroid stimulating hormone during pregnancy, it is recommended to go to the hospital and ask the doctor to make a judgment and give a treatment plan.