The process of fertilized egg formation takes place within 24 hours after intercourse, while the egg meets the sperm about 1-2 hours after intercourse, up to 6 hours. The male sperm enters the woman’s vagina and moves rapidly forward, relying on the swing of the sperm tail, to the woman’s uterine cavity and eventually to the abdomen of the fallopian tube, where the woman’s discharged egg has long been waiting to meet the sperm. If the egg and sperm meet when they are both very vigorous, a fertilized egg can be formed. If the egg and sperm meet when one of them is significantly less energetic, fertilization may fail.