Ectopic Pregnancy
Obstetrics & Gynecology
Illness script · Obstetrics & Gynecology
Ectopic Pregnancy
Implantation of a fertilized ovum outside the uterine cavity, most commonly in the fallopian tube (~95%).
This illness script for Ectopic Pregnancy covers predisposing factors, classic presentation, mechanism, workup, management, and the clinical pivots that separate it from look-alikes—written for USMLE Step 1 and clerkship reasoning.
01
Predisposing factors
- Prior ectopic pregnancy (strongest single risk factor, ~10× increased risk)
- Prior pelvic inflammatory disease / salpingitis (Chlamydia, Gonorrhea)
- Prior tubal surgery or ligation
- IUD use (lowers overall pregnancy risk but raises ectopic fraction if pregnant)
- Assisted reproductive technology (IVF)
- Smoking impairs tubal motility
02
Presentation
- Classic triad: amenorrhea + unilateral pelvic pain + vaginal bleeding
- Pain often begins dull/crampy, becomes sharp and severe with rupture
- Cervical motion tenderness (chandelier sign) on bimanual exam
- Adnexal tenderness or mass on exam
- Rupture: sudden severe pain, shoulder tip pain (diaphragmatic irritation from hemoperitoneum), syncope, hypotension
- Uterus is normal size or slightly enlarged
03
Pathophysiology
- Impaired ovum transport → implantation in fallopian tube
- Trophoblast invades thin tubal wall → progressive distension
- Tubal rupture at ~6–8 weeks → massive hemorrhage and hemoperitoneum
- Rising β-hCG is inappropriately low and fails to double appropriately (every 48h)
04
Diagnostics
- Serum β-hCG: first test — positive in virtually all ectopics
- Transvaginal ultrasound (TVUS): first-line imaging — empty uterus with adnexal mass
- Discriminatory zone: β-hCG >1500–2000 mIU/mL + no IUP on TVUS = presumed ectopic
- Serial β-hCG rising <66% over 48h supports ectopic (vs. normal IUP)
- Culdocentesis (historical): non-clotting blood in cul-de-sac indicates hemoperitoneum
05
Management
- Unstable (ruptured): emergent surgical exploration — salpingectomy
- Stable, unruptured, small (<3.5 cm), β-hCG <5000: methotrexate (MTX) IM single-dose
- MTX contraindications: breastfeeding, hepatic/renal disease, immunodeficiency, cardiac activity on US
- Post-MTX: serial β-hCG weekly until undetectable; avoid NSAIDs (↓efficacy), folic acid supplements
- Rh-negative patients: Rh immunoglobulin (RhoGAM) regardless of management route
06
Clinical pivots
How to separate this script from the look-alikes that show up on exams and on the wards.
Threatened/Inevitable Abortion
IUP confirmed on TVUS; ectopic has empty uterus on ultrasound at discriminatory zone
Corpus Luteum Cyst / Ruptured Ovarian Cyst
β-hCG is negative; no pregnancy involved
Appendicitis
Positive β-hCG and adnexal location on TVUS distinguish ectopic; appendicitis lacks pregnancy
Heterotopic Pregnancy
Simultaneous IUP + ectopic; IUP on US does NOT exclude ectopic in IVF patients
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Educational use only. This illness script is a study framework, not medical advice. Confirm decisions with current guidelines and your clinical supervisors.