It is impossible for a woman to detect pregnancy after 3 days of intercourse. This is because even if ovulation occurs at the time of intercourse or before intercourse, and the patient is able to get pregnant during intercourse, it takes about a week for the sperm and egg to form a fertilized egg and to implant. It takes about a week for the sperm and egg to form the fertilized egg and to implant. Before the fertilized egg implantation, the levels of estrogen, progesterone, prolactin and chorionic gonadotropin in a woman’s body don’t change, so there is no way to tell if the patient is pregnant by checking the above mentioned biochemical indexes. After the fertilized egg has been laid, it takes about 1-2 days for the levels of estrogen, progesterone, prolactin, and HCG in the blood to rise sharply, and it is only by checking the blood chorionic gonadotropin and progesterone that the patient can be detected to be pregnant or not.