title: History and physical examination to estimate the risk of ectopic pregnancy: validation of a clinical prediction model.
abstract: 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Emergency Medicine, Naval Medical Center, San Diego, CA 92134-1005, USA. rgbuckley@rota.med.navy.mil
authors.forename: R G
authors.initials: RG
authors.lastname: Buckley
authors.forename: K J
authors.initials: KJ
authors.lastname: King
authors.forename: J D
authors.initials: JD
authors.lastname: Disney
authors.forename: J D
authors.initials: JD
authors.lastname: Gorman
authors.forename: J H
authors.initials: JH
authors.lastname: Klausen
mesh_terms: D000328:Adult; D003661:Decision Support Techniques; D005260:Female; D006801:Humans; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D011271:Pregnancy, Ectopic / Q000175:diagnosis*; D018566:Pregnancy, High-Risk; D011446:Prospective Studies; D015203:Reproducibility of Results; D018570:Risk Assessment; D012680:Sensitivity and Specificity