When a woman ovulates and sex occurs during ovulation, the union of the egg and sperm will mostly occur within a few hours after ovulation, usually no more than 24 hours. With normal reproductive function in both sexes, sperm enter the vagina and the active sperm will pass through the cervical canal and uterine cavity and enter the fallopian tubes, a process that takes about 7-8 hours. After the follicle is expelled from the ovary, it enters the fallopian tube via the umbilical end of the fallopian tube. This process takes 12-16 hours, and the egg meets the sperm in the abdomen of the fallopian tube and unites to form a fertilized egg, which completes fertilization. The movement of the sperm and egg may occur simultaneously or sequentially, but this does not affect the formation of the fertilized egg. After fertilization, the fertilized egg stays in the fallopian tube for about one day and then moves towards the uterine cavity with the help of the peristalsis of the fallopian tube, where it settles and develops into an embryo and continues to develop into a fetus.