Pregnancy, Ectopic

An ectopic pregnancy is any implantation of a fertilized ovum at a site other than the endometrial lining of the uterus. Virtually all ectopic pregnancies are considered nonviable and are at risk of eventual rupture. Rupture of an ectopic pregnancy and resulting hemorrhage is one of the leading causes of first-trimester maternal death in the developed world; therefore, early diagnosis and treatment (before rupture) is important to prevent morbidity and mortality.^[1]
An endovaginal sonogram demonstrates an early ectopic pregnancy. An echogenic ring (tubal ring) found outside of the uterus can be seen in this view. Pregnancy, ectopic. An endovaginal sonogram reveals an intrauterine pregnancy at approximately 6 weeks. A yolk sac (ys), gestational sac (gs), and fetal pole (fp) are depicted.

The faulty implantation that occurs in ectopic pregnancy occurs because of a defect in the anatomy or normal function of either the fallopian tube (as in surgical or infectious scarring), the ovary (as in women undergoing fertility treatments), or the uterus (as in cases of bicornuate uterus, cesarean delivery scar).
Reflecting this, about 95% of ectopic pregnancies occur in the fallopian tube — 70% in the ampulla; 12%, isthmus; 11.1%, fimbria; and 2.4%, interstitium (or cornual region of the uterus). Some ectopic pregnancies implant in the cervix (< 1%), in prior cesarean delivery scars, or in a rudimentary uterine horn; although these may be technically in the uterus, they are not considered normal intrauterine pregnancies. About 3.2% of ectopic pregnancies occur in the ovary, and 1.3% occur in the abdomen.^[2] About 80% of ectopic pregnancies are found on the same side as the corpus luteum (the old ruptured follicle), when present.^[3] In the absence of modern prenatal care, abdominal pregnancies can present at an advanced stage (>28 wk) and have the potential for catastrophic rupture and bleeding.^[4]