LOL per Wikipedia: Causes There are a number of risk factors for ectopic pregnancies. However, in as many as one third [2]to one half [3] of ectopic pregnancies, no risk factors can be identified. Risk factors include: pelvic inflammatory disease, infertility, those who have been exposed to DES, tubal surgery, smoking, previous ectopic pregnancy, multiple sexual partners, and tubal ligation. [4]