The diagnostic effectiveness of an initial transvaginal scan in detecting ectopic pregnancy

BACKGROUND: To determine the effectiveness of an initial transvaginal ultrasound scan (TVS) in the detection of ectopic pregnancy in consecutive women attending an early pregnancy unit (EPU). METHODS: This was a prospective observational study. Unselected women attending a dedicated EPU underwent a TVS. Women were classified as having an intrauterine pregnancy (IUP), ectopic pregnancy or pregnancy of unknown location (PUL). Women with a PUL were followed up until the final location of the pregnancy was determined. The sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) with 95% confidence intervals (CIs) for the initial TVS in the diagnosis of ectopic pregnancy were calculated. RESULTS: During a one-year study period, 5318 consecutive women attended the EPU. Outcome data were available for 5240 (98.5 %) women. Of these, the initial TVS showed an IUP in 4693 (89.6 %) cases and an ectopic pregnancy in 91 (1.7 %) cases. The remaining 456 (8.7 %) women were classified as PUL, and of these 31 (6.8 %) were subsequently found to have ectopic pregnancies. The overall sensitivity of the initial TVS in the diagnosis of ectopic pregnancy was 73.9 % (95 % CI: 65.1-81.6) with a specificity of 99.9 % (95 % CI: 99.8-100), a PPV of 96.7% (95% CI: 90.7-99.3) and an NPV of 99.4% (95% CI: 99.2-99.6). CONCLUSIONS: In unselected women attending an EPU, pregnancy location can be diagnosed accurately in over 90 % of all pregnancies and in 73.9% of ectopic pregnancies with a single TVS.