Risk factors for ectopic pregnancy

Pelvic inflammatory disease (PID)
Rate of ectopic pregnancy in women with previous known PID is increased 6-10 times higher than in women with no previous history of PID.
A published study of 745 women with one or more episodes of PID that attempted to conceive showed that 16% were infertile from tubal occlusion. Of those that conceived, 6.4% had ectopic pregnancies.
Pelvic inflammatory disease is usually caused by invasion of either gonorrhea or chlamydia from the cervix up to the uterus and tubes. The infection in these tissues causes an intense inflammatory response. Bacteria, white blood cells and other fluids (pus) fill the tubes as the body combats the infection. Eventually, the body wins and the bacteria are controlled and destroyed. However, during the healing process the delicate inner lining of the tubes (tubal mucosa) is permanently scarred. The end of the tube by the ovaries may become partially or completely blocked, and scar tissue often forms on the outside of the tubes and ovaries. All of these factors can impact ovarian or tubal function and the chances for conception in the future. If pelvic inflammatory disease is treated very early and aggressively with IV antibiotics, the tubal damage might be minimized, and fertility maintained.
Progestin contraceptives
Progesterone-bearing IUD's and ectopics: 16% of pregnancies were ectopics.
Pregnancy after tubal ligation
Tubal sterilization and ectopics: After non-laparoscopic tubal ligation about 12% of pregnancies are ectopic.
After laparoscopic tubal coagulation about 51% of pregnancies are ectopic.
Previous tubal surgery