Sperm can survive for about three days, and of course after a man ejaculates semen into a woman’s vagina, the sperm will leave the semen and travel through the woman’s cervix into the uterine cavity, and some of the sperm in the uterine cavity can travel to the opening of the fallopian tube and travel through the opening of the tube to enter the inside of the tube, where they will remain for a certain period of time. So, if there is a history of coitus about three days before ovulation, it is very likely that some of the sperm will be waiting in the fallopian tube after three days. If you have intercourse at that time, it is very likely that within 12-24 hours, the umbrella of the fallopian tube will be able to catch a normal, healthy, mature egg and rely on the peristalsis of the fallopian tube as well as the swinging of the cilia in the fallopian tube to transport the egg towards the uterine cavity, thus causing the egg and the sperm to meet in the lumen of the fallopian tube and have the opportunity to unite to form a fertilized egg.