An ectopic pregnancy occurs when a fertilized egg implants and grows outside the main cavity of the uterus. An ectopic pregnancy most often occurs in a fallopian tube, which carries eggs from the ovaries to the uterus. This type of ectopic pregnancy is called a tubal pregnancy. an ectopic pregnancy happens because the fertilized egg wasn't able to move down the fallopian tube quickly enough. An infection or inflammation in the tube can cause it to be partially or completely blocked. This is commonly caused by pelvic inflammatory disease (PID). An ectopic pregnancy occurs when a pregnancy develops outside of the womb, usually in one of the fallopian tubes. An ectopic embryo will not survive and the pregnancy will miscarry.