Low thyroid stimulating hormone in early pregnancy may be a normal phenomenon in early pregnancy, but it may also be caused by transient thyrotoxicosis of pregnancy, etc. 1. Physiological phenomenon: due to the action of human chorionic gonadotropin, the upper and lower limits of the reference range of serum thyroid stimulating hormone in early pregnancy will decrease to different degrees, and the lower limit of thyroid stimulating hormone in a small number of pregnant women is even lower than the detectable level. However, this is a normal physiological phenomenon and does not require special treatment. 2. Transient thyrotoxicosis in pregnancy: serum thyrotropin is lower than the lower limit of the pregnancy-specific reference range (or 0.1mU/L), free thyroxine is greater than the upper limit of the pregnancy-specific reference range, and after exclusion of hyperthyroidism, the diagnosis of transient thyrotoxicosis in pregnancy can be made. Low thyroid stimulating hormone in early pregnancy may be caused by Graves’ disease or other causes other than those mentioned above, and you should go to your local hospital and follow the doctor’s instructions.