Pitfalls in diagnosis of interstitial pregnancy.

Background: To determine the incidence and reasons for misdiagnosis in interstitial ectopic pregnancy.

Methods: We conducted a retrospective study from 1990 to 2001. Women with interstitial pregnancy were identified and their case records retrieved and reviewed. Reasons for delay in diagnosis and associated morbidity were recorded.

Results: Thirty-six women were diagnosed as having interstitial pregnancy during the study period. Initial diagnosis was incorrect in 15 cases (41.7%). In 14 cases, the interstitial pregnancies were mistaken as intrauterine pregnancy. These misdiagnoses resulted in six inappropriate surgical procedures (evacuation of uterus) being performed and led to rupture of interstitial pregnancy in eight women. In two women, the interstitial pregnancy was mistaken as normal intrauterine pregnancy while the uterus itself was thought to be a cervical fibroid. In both cases, the interstitial pregnancies ruptured at 18-20 weeks of gestation.

Conclusion: Despite advances in sonographic skills and equipment and the availability of beta-human chorionic gonadotropin (hCG) monitoring, misdiagnosis of interstitial pregnancy still occurs frequently. Clinicians should be aware of the limitations of various investigations and maintain a high index of suspicion.