On the third day after ovulation, if the sperm and the egg have already united to form a fertilized egg, there are no clinical symptoms. This is because the fertilized egg is still at the stage of germ cells, which are relatively small and are in the fallopian tubes and have not yet entered the uterine cavity. Only after the fertilized egg enters the uterine cavity and settles, the trophoblast cells start to secrete blood HCG, and with the increase of blood HCG and estrogen, the corresponding symptoms will appear. For example, it is around the 25th day of post-ovulation intercourse that gastrointestinal reactions such as more salivation, anorexia, nausea, vomiting, and also local changes in the breasts, which will increase in size and mild pain, will appear clinically.