The process of sperm-egg union is called fertilization, which usually takes 24 hours, and the fertilized egg moves into the uterine cavity about 3 days after fertilization. The sperm is transported through the vagina, cervix and fallopian tubes, relying on the peristalsis of the fallopian tube muscles, the oscillation of the mucosal cilia and the secretion of mucus cells to reach the abdomen of the fallopian tube and unite with the egg, a process called fertilization. The process usually starts within 12 hours after intercourse and takes 24 hours to complete, when the chromosomes of the sperm and egg fuse together. The fertilized egg gradually moves into the uterine cavity after about 3 days and settles at a suitable site. The process of settling is completed in about 8 days and the basal cell layer starts to secrete HCG. Therefore, usually, 8-10 days after fertilization, a woman can have a blood test for HCG to diagnose early pregnancy, or she can use an early pregnancy test about 1 week after menstruation.