There are a few, but the highest one is having a had an ectopic pregnancy before. There is a 33 percent recurrence risk!
Anything that changes the anatomy of the fallopian tube makes an ectopic pregnancy more likely. This is because altered anatomy makes it harder for an egg to travel to its normal implantation site in the uterus. This can be caused by a previous ectopic pregnancy, as well as a prior infection with gonorrhea or chlamydia, or a history of pelvic inflammatory diseases (also called PID). These infections can cause scarring in the fallopian tubes, which is why they increase your risk. Having surgery on your tubes (such as with a tubal ligation) also makes an ectopic pregnancy more likely. Other unique risk factors include undergoing in vitro fertilization or smoking.