History and physical examination to estimate the risk of ectopic pregnancy: validation of a clinical prediction model

Ann Emerg Med. 1999 Nov;34(5):589-94. doi: 10.1016/s0196-0644(99)70160-5.


Study objective: To prospectively validate a clinical prediction model for ectopic pregnancy (EP).

Methods: Prospective cohort with 14-month derivation and 12-month validation phases. All hemodynamically stable, first-trimester patients with abdominal pain or vaginal bleeding who presented to a military teaching hospital emergency department underwent follow-up until an outcome of intrauterine pregnancy (IUP) or EP was established. Patients were separated into the high-risk group, defined as having either peritoneal signs or definite cervical motion tenderness; intermediate-risk group, defined as the presence of pain or tenderness, other than midline cramping, plus absence of fetal heart tones, and absence of tissue visible at the cervical os; and low-risk group (neither high- nor intermediate-risk) using recursive partitioning.

Results: Summarizing both phases, 915 patients had 845 (93%) IUPs and 70 (7.6%) EPs, with 18 (1.9%) lost to follow-up. The clinical prediction model classified 75 (8.2%) into the high-risk group (sensitivity 31%, 95% confidence interval [CI] 21% to 44%; specificity 94%, 95% CI 92% to 95%); and 644 (70%) in the intermediate-risk group (sensitivity 98%, 95% CI 89% to 100%; specificity 25%, 95% CI 22% to 29%). The remaining 196 (21%) patients who met neither high-risk nor intermediate-risk criteria were classified into the low-risk group. On the basis of EP prevalence of 7.7%, the risk of EP was less than 1% (95% CI 0% to 3%) for the low-risk group, 7% (95% CI 5% to 10%) for the intermediate-risk group, and 29% (95% CI 19% to 41%) for the high-risk group.

Conclusion: This clinical prediction model is useful for estimating the risk of EP in first-trimester patients, particularly when ancillary testing is equivocal or not readily available.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Adult
  • Decision Support Techniques*
  • Female
  • Humans
  • Pregnancy
  • Pregnancy Trimester, First
  • Pregnancy, Ectopic / diagnosis*
  • Pregnancy, High-Risk
  • Prospective Studies
  • Reproducibility of Results
  • Risk Assessment
  • Sensitivity and Specificity