An ectopic pregnancy develops as the result of the blastocyst implanting somewhere other than in the endometrium of the uterus. Sites of an ectopic pregnancy (Fig. 17-1) are the fallopian tube, ovary, cervix, or abdominal cavity. The majority of ectopic pregnancies (97%) are located in the fallopian tube, with 0.5% located on an ovary, 0.3% on the cervix, and 1.5% in the abdominal cavity (Attar, 2004; ACOG, 2008).
Of all tubal ectopic pregnancies, 55% are located in the ampulla, or largest portion of the tube. The next most common site is the isthmus, or the narrow part of the tube that connects the interstitium to the ampullar portion. Three percent of ectopic pregnancies are located in the interstitium, which is the muscular portion of the tube adjacent to the uterine cavity. Rarely does the ectopic pregnancy locate in the fimbria or terminal end of the tube (Lozeau and Potter, 2005; Cunningham and others, 2010). The outcome and gestational length of the tubal ectopic pregnancy are influenced by its location in the fallopian tube.