How do you diagnose an ectopic pregnancy?

Diagnosis of Ectopic Pregnancy

Transvaginal ultrasound (TVUS) combined with serum quantitative β-hCG testing is the most effective diagnostic approach for ectopic pregnancy in any woman of reproductive age with pelvic pain and/or vaginal bleeding with a positive pregnancy test. 1

Clinical Presentation

• Abdominal/pelvic pain
• Vaginal bleeding
• Amenorrhea
• Syncope or hypotension (in cases of rupture)

Diagnostic Algorithm

Step 1: Pregnancy Confirmation

• Perform a sensitive urine or serum β-hCG test in any woman of reproductive age presenting with abdominal pain or vaginal bleeding

Step 2: Ultrasound Evaluation

• TVUS is the single best diagnostic modality for evaluating patients with suspected ectopic pregnancy 2
• A meta-analysis of 14 studies with 12,101 patients showed a positive likelihood ratio of 111 for finding an adnexal mass without an intrauterine pregnancy on TVUS 2

Definitive Ultrasound Findings of Ectopic Pregnancy:

• Extrauterine gestational sac with live embryo (100% specific but uncommon) 2
• "Tubal ring" - extrauterine mass with fluid center and hyperechoic periphery 2, 1
• Nonspecific heterogeneous adnexal mass (most common finding) 1

Suggestive Ultrasound Findings:

• Empty uterus with β-hCG >3,000 mIU/mL 2, 1
• Abnormal free fluid (more than trace amount or containing echoes) 2
• Endometrial thickness <8 mm with positive pregnancy test 2

Step 3: β-hCG Correlation

• Discriminatory zone: A gestational sac should be visible on TVUS when β-hCG >3,000 mIU/mL 2, 1
• In a stable patient, diagnosis of ectopic pregnancy should not be made at β-hCG ≤3,000 mIU/mL without additional findings 2
• Serial β-hCG measurements are more informative than single values:
  • Normal rise is at least 53% over 48 hours in viable intrauterine pregnancy 1
  • Abnormal rise or plateau suggests ectopic pregnancy or non-viable intrauterine pregnancy

Pregnancy of Unknown Location (PUL)

PUL is defined as a positive pregnancy test with no evidence of intrauterine or extrauterine pregnancy on ultrasound 1

• 7-20% of PUL cases are ultimately diagnosed as ectopic pregnancies 1
• Management requires:
  • Serial β-hCG measurements (48-hour intervals)
  • Repeat TVUS in 7-10 days if patient remains stable
  • Close clinical monitoring

Distinguishing Corpus Luteum from Ectopic Pregnancy

• Corpus luteum appears as a <3 cm cystic lesion with thick wall or rounded hypoechoic lesion 2
• Key assessment is whether the mass is inside the ovary (corpus luteum) or outside the ovary (potential ectopic) 1
• Apply gentle pressure with the transvaginal transducer to see if the mass moves with the ovary 2, 1
• Ectopic pregnancies are located ipsilateral to corpus luteum in 70-80% of cases 2, 1

Non-Tubal Ectopic Locations

• Interstitial, cervical, and cesarean section scar are the most common non-tubal locations 2, 1
• Three-dimensional ultrasound may help diagnose interstitial pregnancy 2
• Heterotopic pregnancy (simultaneous intrauterine and extrauterine) is rare but more common with assisted reproduction 1

Common Pitfalls to Avoid

• Relying solely on the absence of intrauterine pregnancy for diagnosis can lead to false positives 1
• Using transabdominal ultrasound alone has lower sensitivity 1
• Making a diagnosis based on a single β-hCG measurement rather than serial measurements 1
• Failing to evaluate the adnexa when an intrauterine pregnancy is seen (can miss heterotopic pregnancy) 1
• Misinterpreting corpus luteum as ectopic pregnancy or vice versa 1
• Diagnosing ectopic pregnancy based solely on β-hCG levels without ultrasound findings 2

Special Considerations

• Unstable patients with suspected ruptured ectopic pregnancy require immediate resuscitation and gynecologic consultation 3
• Diagnostic uterine curettage may be appropriate in stable patients with non-diagnostic ultrasound and abnormal β-hCG trends 4
• TVUS sensitivity for ectopic pregnancy is lower with β-hCG <2,000 mIU/mL (34.3% sensitivity) compared to higher levels (75.9% sensitivity) 2

By following this diagnostic algorithm, clinicians can promptly identify ectopic pregnancies, reducing the risk of rupture and improving patient outcomes.