HCG is an important marker representing pregnancy, which usually starts to be secreted 6-10 days after fertilization and gradually disappears around 2 weeks after delivery. The reference range of HCG in pregnancy is not completely consistent depending on individual differences and pregnancy stages.1. Early Pregnancy: A clear HCG value can usually be detected on the 10th day of pregnancy, HCG secretion is fast in early pregnancy, increasing 1-fold in 1.7-2.0 days on average, and the doubling time can last 3-8 days until HCG reaches the highest level of about 50-100kU/L in 8-10 weeks of pregnancy. If the HCG value increases slowly in early pregnancy, the possibility of miscarriage and ectopic pregnancy is higher; 2. Mid and late pregnancy: HCG value can last 1-2 weeks after reaching the peak, and then start to decline gradually until it reaches the mid and late stage, the HCG value concentration is only 10% of the peak, that is, 5-10kU/L, and can last until the end of delivery. HCG is a water-soluble glycoprotein hormone secreted by syncytial trophoblast cells, which, like thyroid hormone and progesterone, plays an important role in maintaining the stable development of pregnancy and promoting fetal growth and development. Therefore, pregnant women need to have strict and regular checkups during pregnancy to ensure the healthy growth of themselves and their fetus.