The accuracy of determining pregnancy through a blood HCG test is relatively high, generally above 99%. The accuracy of the test is related to the length of pregnancy and the rate of hormone secretion, etc. The chance of detecting pregnancy is around 50%-70% for a relatively short period of 8 days after intercourse. Pregnancy can be basically confirmed by quantifying the value of HCG in the blood, if the level of HCG in the blood is greater than 10 units per liter. After intercourse the sperm and egg form a fertilized egg in the abdomen of the fallopian tube. After about 7 days to complete implantation, the trophoblast cells start to secrete human chorionic gonadotropin. The embryo has just completed implantation after 8 days of intercourse, the secretion of human chorionic gonadotropin is relatively small and the concentration in the blood is relatively low, so it is recommended to go to the hospital to test the HCG value about 10 days after intercourse.