The egg can reach the uterine cavity 4 hours after fertilization, after intercourse the sperm and egg meet in the fallopian tube to form a fertilized egg, most of the fertilized tube can occur within a few hours after ovulation, usually not more than 24h. 30 hours after fertilization the fertilized egg moves slowly towards the uterine cavity under the action of the fallopian tube, the process takes about 3 days, the fertilized egg in the fallopian tube enters the uterine cavity and lays down to form a gestational sac, then development occurs. When the vas deferens moves to the uterine cavity, it is easily affected by many factors, such as tubal inflammation, pelvic inflammatory disease, and the effect of contraceptive pills, which make the peristalsis and cilia wiggling ability of the fallopian tube become poor, and this time will affect the movement of the fertilized egg to the uterine cavity, thus causing the fertilized egg to implant in the fallopian tube and form ectopic pregnancy.