The uterus has a fallopian tube attached to each side. At the end of each fallopian tube are delicate fingerlike projections called fimbriae. These fimbriae function to catch ova (eggs) released from the ovary and help transport the egg(s) down the tube and into the uterus. Sperm actually meet the ovum (egg) in the tube. The resulting early embryo is then wafted down to the uterus where implantation normally occurs. Tiny little hair-like structures inside the fallopian tube called cilia beat rhythmically, also moving the embryo along the tube. If the embryo gets stuck along the way then an ectopic/tubal pregnancy occurs. The embryo grows in the narrow tube until the tube can no longer accommodate it. The tube then ruptures, causing bleeding into the abdomen.
|An opened oviduct with an ectopic pregnancy at about 7 weeks gestational age. Wikipedia|