The most common site is within a Fallopian tube.
Most cases are a result of scarring caused by previous tubal infection or tubal surgery.
Some ectopic pregnancies can be traced to congenital tubal abnormalities, endometriosis , tubal scarring and kinking caused by a ruptured appendix, or scarring caused by previous pelvic 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. The incidence data for ectopic pregnancies ranges from 1 in every 40 to 100 pregnancies.