Ectopic Pregnancy - Diagnostic Criteria

1. Classic Clinical Triad

• Abdominal/pelvic pain - the most common symptom (~90% of cases); may be unilateral, bilateral, sharp, crampy, or dull
• Amenorrhea - missed period or irregular last menstrual period
• Vaginal bleeding - often spotting or light bleeding

• Shoulder tip pain (diaphragmatic irritation from hemoperitoneum)
• Syncope or dizziness with rupture

2. Risk Factors that Raise Pre-test Probability

• Prior ectopic pregnancy
• Prior tubal surgery or sterilization (especially laparoscopic partial salpingectomy, electrodestruction; age <28, 5-15 years post-procedure = very high risk)
• History of pelvic inflammatory disease / salpingitis
• Infertility or assisted reproduction (IVF increases ectopic rate to ~4%)
• IUD in situ (if pregnancy occurs, more likely ectopic)
• Cigarette smoking (dose-dependent; RR up to 3.5 for >20 cigarettes/day)
• Prior pelvic/abdominal surgery

3. Physical Examination Findings

4. Serum β-hCG Criteria

Single Level

• A negative β-hCG effectively excludes ectopic pregnancy
• Absolute levels cannot differentiate ectopic from IUP due to significant overlap
• β-hCG >discriminatory zone with empty uterus on US = suspect ectopic

The Discriminatory Zone

• The β-hCG level above which an IUP should be visible on ultrasound
• Transvaginal US: discriminatory zone traditionally 1,500-2,000 mIU/mL (some centers now use 3,000-3,510 mIU/mL to avoid disrupting a normal IUP)
• Transabdominal US: discriminatory zone ~6,000 mIU/mL
• Important caveat: ACOG advises using up to 3,000 mIU/mL to avoid misdiagnosis; no β-hCG level alone is diagnostic of ectopic
• β-hCG does not correlate with ectopic pregnancy size or location

Serial β-hCG (for pregnancy of unknown location)

• Normal viable IUP: rises at least 35-66% over 48 hours (conservative cut-off 35% to capture >99% of viable IUPs in diverse populations; classic cut-off 66%)
• Ectopic or failing pregnancy: slower rise, plateau, or decline
• Expected decline in spontaneous abortion: 21-35% at 2 days, 60-84% at 7 days
• An 85% drop within 4 days or 95% drop in 7 days = risk of ectopic ~0

5. Serum Progesterone

6. Ultrasound Criteria

Definitive Diagnosis (no further testing needed)

• Embryo with cardiac activity outside the uterus (seen in <10% of ectopics - but diagnostic when present)

High Suspicion Findings on Transvaginal US

Findings that Support (but don't confirm) Ectopic

• Empty uterus with positive β-hCG above discriminatory zone
• Adnexal ring (thick echogenic ring around a sac, seen in <50% of ectopics)
• Pseudogestational sac (centrally located endometrial fluid collection - occurs in 8-29% of ectopics; distinguish from true sac using double decidual sac sign [DDSS])
• Complex or solid adnexal mass
• Free cul-de-sac fluid

Excludes Ectopic (with caveats)

• Unequivocal IUP (yolk sac or embryo with cardiac activity within uterine cavity) - excludes ectopic except in assisted reproduction patients where heterotopic pregnancy risk is up to 1 in 3,000 (general population) or 4% (IVF)
• Gestational sac alone is NOT sufficient to confirm IUP (pseudosac can mimic)

7. Other Diagnostic Modalities

• Laparoscopy: Gold standard - diagnostic and therapeutic; used when US is nondiagnostic
• Uterine curettage (D&C): Useful when pregnancy is nonviable and location uncertain; presence of chorionic villi (float in saline, frond appearance) confirms IUP and excludes ectopic
• Culdocentesis: Largely replaced by US; non-clotting blood on aspiration suggests hemoperitoneum
• MRI: High sensitivity and specificity, but limited by cost and availability

Summary Algorithm

Positive pregnancy test
       ↓
Transvaginal US
       ↓
IUP seen? → Yes → Ectopic excluded (heterotopic rare)
       ↓ No
β-hCG level + serial monitoring
       ↓
>Discriminatory zone + empty uterus → Ectopic strongly suspected
       ↓
<Discriminatory zone → Serial β-hCG q48h
       ↓
Rise <35% or plateau → Ectopic vs. failing IUP → D&C or laparoscopy