In a normal pregnancy, a fertilized egg implants in the lining of the uterus. An ectopic pregnancy occurs when a fertilized egg implants outside of the uterus. Most ectopic pregnancies occur in the fallopian tubes, so the term "tubal pregnancy" is also used. An embryo or fetus located in a fallopian tube cannot survive, can be life-threatening to the woman carrying it, and requires emergency treatment.

Early ectopic pregnancy can sometimes be treated with a medication called methotrexate. This is used to stop the embryo from growing before it ruptures the tube. However, surgery is sometimes needed to remove the ectopic pregnancy from the fallopian tube and also to preserve the tube for future fertility.

Pelvic inflammatory disease (PID) is a common cause of ectopic pregnancy. PID causes inflammation and scarring that can block or twist the tube. Scarring (adhesions) may prevent a fertilized egg from moving down the fallopian tube to the uterus.

Studies show that the risk of an ectopic pregnancy in women who have a history of PID is 6 times greater than in women without a history of PID.¹ Of women who become pregnant after having PID, about 10% have an ectopic pregnancy.²