Case Report of an Interstitial Ectopic Pregnancy

Carol Green, Bradford Teaching Hospital Foundation Trust


An ectopic pregnancy occurs when a fertilised ovum implants outside the uterine cavity. 96% of all ectopic pregnancies will be located in the fallopian tube. Rarely, 3–5% of ectopic pregnancies may present in other locations such as abdominal, cervical, interstitial or ovarian. An interstitial ectopic pregnancy occurs when the fertilised ovum implants in the proximal portion of the fallopian tube located within the myometrium. Transvaginal ultrasound scanning (TVUS) is a good method for early pregnancy assessment owing to the increased image quality. Three-dimensional transvaginal ultrasound (3DUS) may be of benefit and aid diagnosis owing to its increased image resolution.

Case report

37-year-old pregnant patient was referred to early pregnancy assessment unit with vaginal bleeding and back ache. Ultrasound revealed a normal endometrial thickness measuring 4mm, with no evidence of an intrauterine or ectopic pregnancy.

In view of the ultrasound findings and the positive hCG levels the patient underwent a diagnostic laparoscopy to assess for an ectopic pregnancy, which showed no evidence of an ectopic pregnancy. The patient re-presented four weeks later as her pregnancy test remained positive. TVUS again revealed a normal endometrial thickness, however at the right lateral border of the uterus a live ectopic pregnancy was identified.


Owing to the rarity of interstitial pregnancies, this form of ectopic pregnancy can be misdiagnosed as a viable intrauterine pregnancy. Having highly trained sonographers scanning the patient will help reduce misdiagnosis. 3DUS can improve general diagnosis due to the increased image quality. However, in this case there was no sign of pregnancy at the initial ultrasound scan, therefore at this stage using 3DUS would not change the clinical diagnosis. On follow-up TVUS, the pregnancy had developed thus was visible and demonstrated classical signs of an interstitial ectopic pregnancy. Using 3DUS would not have added to the clinical diagnosis.

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