Eccentrically located intrauterine pregnancy misdiagnosed as interstitial ectopic pregnancy.

This is a case report of an eccentrically located intrauterine pregnancy initially diagnosed as an interstitial ectopic pregnancy. Although interstitial ectopic pregnancy represents a well-known pitfall in first-trimester sonography, the common error is to misidentify the ectopic pregnancy as intrauterine, not the reverse. Such an error is potentially catastrophic because it may lead to the inadvertent termination of a viable pregnancy. Although the role of ultrasonography for evaluation of ectopic pregnancy is well established, its diagnostic accuracy for interstitial ectopic pregnancy remains uncertain. Because of this, sonographic findings should be considered suggestive, but not diagnostic, in this setting.