This may be caused by a physical blockage in the tube, or by failure of the tubal epithelium to move the zygote down the tube and into the uterus.
Most cases are a result of scarring caused by previous tubal infection.
Some ectopic pregnancies can be traced to congenital tubal abnormalities, endometriosis , tubal scarring and kinking caused by a ruptured appendix, scarring caused by previous tubal surgery and prior ectopic pregnancies. In a few cases, the cause is unknown. On occasion, a woman will conceive after elective tubal sterilization . Slow movement of the fertilized egg down the fallopian tube can result in tubal implantation. Women who become pregnant despite using the progesterone-only oral contraceptives have a 5 fold increase in the ectopic rate.