On the fifth day after ovulation, the egg is discharged from the ovary and is picked up by the umbilical end of the fallopian tube, where it is caught and transported to the lumen of the fallopian tube, where the egg meets the sperm and the sperm-egg unites to form a fertilized egg. Inside the fallopian tube, the fertilized egg is formed and is transported peristaltically from the fallopian tube to the uterine cavity. Normally, the fallopian tubes should transport the fertilized egg to the uterine cavity on day 3-4 after fertilization, and the fertilized egg will begin to implant on day 6-7 after fertilization. If the fallopian tube does not effectively transport the fertilized egg to the uterine cavity on day 6-7 after fertilization, but remains inside the fallopian tube, the fertilized egg that remains inside the fallopian tube on day 6-7 after fertilization will begin to implant inside the fallopian tube and will form an ectopic pregnancy. Therefore, even if the egg encounters sperm immediately after ovulation, it will not begin to implant until the 6th-7th day after ovulation at the earliest.