Background: Medical management of ectopic pregnancy is effective in selected cases and is recommended to treat interstitial pregnancy to avoid surgery that may limit future fertility. Although successful medical management of interstitial pregnancy has been reported, evidence does not support success rates equal to that in other ectopic locations.
Cases: Four cases of interstitial ectopic pregnancy were identified. Only one of the four was successfully treated with medical therapy. Case 1 was a confirmed, 2.5-cm interstitial pregnancy that failed a multiple-dose methotrexate protocol. Case 2 was an unrecognized interstitial pregnancy that failed single-dose therapy. Case 3 was a rupture of a medically managed interstitial pregnancy despite complete resolution of serum human chorionic gonadotropin. A literature review demonstrated an overall combined failure rate of 35% (7/20).
Conclusion: Compared with an isthmic or ampullary pregnancy, a disproportionate number of patients with interstitial pregnancy fail medical management and require emergency surgery. The presence of a documented interstitial pregnancy is not an absolute contraindication to medical management. Patients should be counseled that medical management of an interstitial pregnancy may not have the same rate of success as it does in other locations in the fallopian tube. Surgery in this case may be the preferred treatment option.