HCG refers to chorionic gonadotropin, and if the embryo develops normally, the value will usually double every other day in early pregnancy, and after doubling, pregnant women who are more sensitive can have obvious early pregnancy reactions. In women with regular menstrual cycles, fertilization usually occurs within 24 hours after ovulation, and 6-7 days after fertilization the fertilized egg will enter the uterine cavity and implant, and HCG (human chorionic gonadotropin) can be detected in the mother’s serum one day after implantation to determine pregnancy. During the first 6 weeks of pregnancy, the level of HCG doubles in about 36-48 hours. The rate of increase in HCG begins to slow down after 6 weeks of pregnancy when the HCG level reaches 6,000-10,000 IU/L. The level peaks at 8-10 weeks of pregnancy. It reaches a peak of about 100,000-200,000 IU/L at 8-10 weeks of gestation, and then declines rapidly for 10 days (about 1-2 weeks), reaching a minimum at about 20 weeks of gestation and continuing until delivery. At 6-8 weeks of pregnancy, the HCG value in women’s body is relatively high, and some pregnant women will have obvious early pregnancy reactions, such as nausea, vomiting, increased body temperature, irritability, drowsiness and fatigue, loss of appetite, breast swelling and pain and other symptoms. There are also some pregnant women who do not have any reaction. Therefore, HCG doubling cannot be judged by early pregnancy reaction.