Use of a β-hCG discriminatory zone with bedside pelvic ultrasonography

Study objective: We seek to assess the performance of the β human chorionic gonadotropin (β-hCG) "discriminatory zone" when using bedside pelvic ultrasonography in the evaluation of symptomatic pregnant emergency department (ED) patients.

Methods: This was a cross-sectional study of bedside pelvic ultrasonography performed on consecutive pregnant patients in the first trimester who presented to the ED with abdominal pain or vaginal bleeding. Patients received pelvic ultrasonography, serum β-hCG testing, and blinded formal radiologic ultrasonography. All patients were followed for 8 weeks to determine outcomes. The sensitivity and specificity of a discriminatory β-hCG level of 3,000 mIU/mL for the diagnosis of ectopic pregnancy were calculated for patients without an intrauterine pregnancy visualized by bedside ultrasonography.

Results: Thirty-six faculty physicians performed bedside pelvic ultrasonography on 256 patients. There were 161 cases with a confirmed visualizable intrauterine pregnancy and 29 ectopic pregnancies. Bedside ultrasonography identified 115 intrauterine pregnancies. The range of β-hCG for cases of confirmed visualizable intrauterine pregnancy with a nondiagnostic bedside ultrasonography was 15 mIU/mL to 123,368 mIU/mL (median 6,633; interquartile range 1,551 to 32,699). For patients with nondiagnostic bedside ultrasonography, using a discriminatory β-hCG level of 3,000 mIU/mL to further assess for ectopic pregnancy showed sensitivity of 35% (95% confidence interval [CI] 18% to 54%) and specificity of 58% (95% CI 48% to 67%). Finally, the overall sensitivity of bedside pelvic ultrasonography for the detection of intrauterine pregnancy was 71% (95% CI 63% to 78%), and the specificity was 99% (95% CI 94% to 100%).

Conclusion: When bedside pelvic ultrasonography does not demonstrate an intrauterine pregnancy, serum β-hCG level is not helpful in differentiating intrauterine from ectopic pregnancy in symptomatic ED patients.