In tubal ectopic pregnancy, implantation is typically in the wall of the tube, in the connective tissue beneath the serosa. There may be little or no decidual reaction and minimal defense against the permeating trophoblast. The trophoblast invades blood vessels to cause local hemorrhage. A hematoma in the subserosal space enlarges as pregnancy progresses. Distention of the tube then predisposes to rupture.

Bleeding is of uterine origin and is caused by endometrial involution and decidual sloughing. Atypical changes in the endometrium may be suggestive of ectopic pregnancy. The Arias-Stella reaction consists of hyperchromatic, hypertrophic, irregularly-shaped nuclei, and foamy, vacuolated cytoplasm. These changes can also be seen in normal pregnancy and in miscarriage, and are therefore not diagnostic of ectopic pregnancy.

Occasionally, endometrial tissue may be passed as a so-called decidual cast. Superficial secretory endometrium usually is present, but no trophoblastic cells are seen. Grossly, this can be confused with passage of products of conception and spontaneous abortion.

Prevention

Prevention of sexually transmitted disease, with early and vigorous treatment of cases that do occur, may avoid tubal damage with subsequent ectopic pregnancy. Other risk factors for ectopic pregnancy are more difficult to control. Early diagnosis of unruptured tubal pregnancy by maintaining a high index of suspicion, and liberally using β-hCG titers, ultrasound, and laparoscopy will minimize potential problems from hemorrhage, infertility, and extensive surgery.