Definition and Incidence of Ectopic Pregnancy An ectopic pregnancy is when a fertilized egg implants outside the uterus, most commonly in the fallopian tube. The incidence of ectopic pregnancy increases with age. Its incidence rate can be as high as more than 10% among women with untreated primary infertility. The combination of multiple factors leads to the occurrence of ectopic pregnancy. The occurrence of ectopic pregnancy is not caused by a single factor, but is caused by multiple synergistic effects. Among them, fallopian tube dysfunction is one of the most important causes. Edema or other lesions in the wall of the fallopian tube make it narrow or blocked, causing the fertilized egg to be unable to move into the uterine cavity and remain in the fallopian tube.