PURPOSE: Visualization of an intrauterine pregnancy with transvaginal ultrasound virtually excludes an ectopic pregnancy. However, findings that might lower patients' risk for ectopic pregnancy have not been extensively investigated. We prospectively performed transvaginal color flow/image-directed Doppler imaging of the endometrium to determine the predictive value of endometrial blood flow for excluding ectopic pregnancy. MATERIALS AND METHODS: From April 1994 to August 1995, 211 consecutive women underwent transvaginal ultrasound examination to exclude an ectopic pregnancy. Color flow/image-directed Doppler imaging of the endometrium was performed on each patient. Flow was considered to be present only if a Doppler signal could be obtained with the cursor located completely within the endometrium. All Doppler imaging parameters were optimized for each patient. Resistive indices were obtained if arterial signal was present, and receiver operator characteristic curves were constructed for RI and peak systolic velocity. Findings were correlated with surgical and pathology results. RESULTS: Of 211 total patients, there were 55 ectopic pregnancies (52 diagnosed for a sensitivity of 95%), 89 incomplete spontaneous abortions, 40 completed spontaneous abortions, and 27 intrauterine pregnancies. Of 55 ectopic pregnancies diagnosed with real time imaging, 9 had areas of endometrial blood flow (6 venous, 3 arterial), and 46 did not. Of the 156 patients that did not have an ectopic pregnancy, 107 had arterial blood flow within the endometrium, and 49 had no flow. Using only cases with arterial signal, the negative predictive value of endometrial blood flow for excluding an ectopic pregnancy was 97% (107/107 + 3). The optimal cutoff values (5% false-positive rate) for peak systolic velocity and refractive index (RI) were 15 cm/s and 0.55. CONCLUSIONS: Arterial blood flow within the endometrium lowers the risk for ectopic pregnancy even when other findings that might indicate a high risk are present. Venous flow within the endometrium does not exclude an ectopic pregnancy.