An ectopic pregnancy happens when a fertilized egg implants outside of your uterus. The egg is meant to travel down your fallopian tubes and embed itself into the wall of your uterus, where it can develop. In an ectopic pregnancy, the egg implants in one of the structures along the way. The most common place this can happen is inside your fallopian tubes. The majority of ectopic pregnancies happen here — about 90%.