The method used to detect pregnancy 8-10 days after intercourse is to draw blood for HCG, which is called human chorionic gonadotropin, a protein hormone secreted by the trophoblast of the placenta. The placenta does not begin to secrete HCG until the seventh day after the formation of a fertilized egg, which means that an elevated level of HCG must be detected in the mother’s blood on the eighth day after the formation of a fertilized egg in order to determine whether or not she is pregnant. After the egg is discharged, it does not necessarily meet the sperm right away. After the egg is discharged, it can wait for 1-2 days in the fallopian tube, waiting for the sperm to enter the fallopian tube to be able to combine. Therefore, it is recommended to have an HCG blood test around 10 days after sexual intercourse to prove pregnancy.