USMLE Prep - Medical Reference Library

Ectopic Pregnancy — β‑hCG/Ultrasound Algorithm, Methotrexate Criteria, and Surgical Management

System: Obstetrics Gynecology • Reviewed: Sep 1, 2025 • Step 1Step 2Step 3

Synopsis:

Suspect ectopic with abdominal pain, vaginal bleeding, and positive pregnancy test. Use β‑hCG and transvaginal ultrasound to determine location; select methotrexate for stable, reliable patients meeting criteria; otherwise proceed to laparoscopic salpingostomy/salpingectomy. Rhogam for Rh‑negative patients.

Key Points

  • Use the highest‑yield diagnostic test early; do not let testing delay time‑critical therapy.
  • Set objective targets (hemodynamic, neurologic, respiratory) and reassess frequently.
  • Plan definitive source control or disease‑specific therapy when indicated; document follow‑up and patient education.

Algorithm

  1. Stabilize; obtain TVUS and quantitative β‑hCG; determine if above discriminatory zone.
  2. If unstable or ruptured → immediate surgery.
  3. If stable and meets criteria → single‑dose methotrexate; schedule day 4/7 β‑hCG checks and counsel on ectopic precautions.
  4. If not a candidate or fails MTX → laparoscopic management (salpingostomy/salpingectomy).
  5. Ensure Rhogam for Rh‑negative; arrange close OB follow‑up and contraception counseling.

Clinical Synopsis & Reasoning

Suspect ectopic with abdominal pain, vaginal bleeding, and positive pregnancy test. Use β‑hCG and transvaginal ultrasound to determine location; select methotrexate for stable, reliable patients meeting criteria; otherwise proceed to laparoscopic salpingostomy/salpingectomy. Rhogam for Rh‑negative patients.


Treatment Strategy & Disposition

Stabilize ABCs. Initiate guideline‑concordant first‑line therapy with precise dosing and continuous monitoring. Escalate to advanced/procedural interventions based on explicit failure criteria. Define ICU, step‑down, and ward disposition triggers; involve specialty teams early.


Epidemiology / Risk Factors

  • Risk varies by comorbidity and precipitants; see citations for condition‑specific data.

Investigations

TestRole / RationaleTypical FindingsNotes
Transvaginal ultrasoundLocalizationAdnexal mass; empty uterus above discriminatory zone
Serial β‑hCGTrajectoryRise/plateau inconsistent with IUPGuide management
CBC/type & screenSafetyAnemia; Rh statusGive Rhogam if Rh‑negative

Pharmacology

Medication/InterventionMechanismOnsetRole in TherapyLimitations
Methotrexate 50 mg/m2 IM (single‑dose protocol)AntimetaboliteDaysFor stable patients meeting criteria (small mass, low β‑hCG, no fetal cardiac activity, reliable follow‑up)Contraindicated in renal/hepatic disease, breastfeeding
Analgesia/antiemeticsSupportiveHoursSymptom control
Rh(D) immune globulinImmuneHoursRh‑negative patientsStandard dosing per GA

Prognosis / Complications

  • Outcome depends on timeliness of diagnosis and definitive therapy; monitor for complications.

Patient Education / Counseling

  • Provide red‑flag education, adherence guidance, and explicit return precautions; arrange timely specialty follow‑up.

References

  1. ACOG Practice Bulletin: Tubal Ectopic Pregnancy (updated) — Link