During pregnancy, thyroid hormones undergo significant changes including production, circulation and metabolism, coming to a new balance with the vary of human chorionic gonadotropin(hCG), thyroid binding globulin(TBG) and iodine metabolism, which makes the thyroid hormones different from those of non-pregnant women. Once the balance cannot be established or broken, it can lead to a variaty of thyroid diseases which result in lots of adverse obstetric and fetal outcomes threated to maternal and child health. Consinderring that, the domestic and foreign guidelines all recommend that regions should establish trimester-specific thyroid function reference intervals. Due to the differences in race, iodine status, research methods, etc., the reference intervals have been established differently in various countries and regions.