HCG, or human chorionic gonadotropin, can be detected as a significant increase in serum HCG about 10 days after successful fertilization. In women of childbearing age, the level of HCG in the blood is very low in the non-pregnant state and is usually not detectable by blood tests. The chorionic trophoblast cells begin to secrete HCG on the 6th day after successful fertilization, and HCG can be detected in the mother’s blood 10 days after successful fertilization, which is currently the most sensitive method for clinical diagnosis of early pregnancy. After the embryo is laid, the level of HCG in the blood of pregnant women increases significantly and reaches a peak in the 8th week of pregnancy, after which it can be maintained until the 12th week and then decreases rapidly until the 18th to 20th week when the level of HCG remains stable, and the level of HCG in the blood of pregnant women in the middle and late stages of pregnancy is only about 10% of the peak value. The level of HCG in a pregnant woman’s blood may also be affected by other factors, and the time at which HCG is detected in the blood may vary depending on the specific condition of the pregnant woman.