How to Diagnose Ectopic Pregnancy
Transvaginal ultrasound combined with serum β-hCG levels is the diagnostic approach for suspected ectopic pregnancy, with transvaginal ultrasound being the single best diagnostic modality (positive likelihood ratio of 111 for adnexal mass without intrauterine pregnancy). 1, 2
Initial Diagnostic Workup
When evaluating any woman of reproductive age with abdominal pain, vaginal bleeding, or amenorrhea, immediately obtain:
- Quantitative serum β-hCG level 3, 4
- Transvaginal ultrasound (TVUS) - perform regardless of β-hCG level 1, 4
- Blood type and Rh status 4
- Complete blood count if rupture suspected 5
Ultrasound Diagnostic Criteria
Definitive Findings for Ectopic Pregnancy
- Extrauterine gestational sac with live embryo - 100% specific but uncommon 3
- Yolk sac or fetal pole visualized outside the uterus - diagnostic 6
- "Tubal ring" - extrauterine mass with fluid center and hyperechoic periphery 1, 3
Highly Suggestive Findings
- Heterogeneous adnexal mass without identifiable gestational sac - most common sonographic finding 3
- Free pelvic fluid with internal echoes (suggesting blood), even without identified extraovarian mass 3, 5
- Absence of intrauterine pregnancy when β-hCG >3,000 mIU/mL - strongly suggestive but not diagnostic 1, 3, 6
Key Technical Points
- Examine the adnexa carefully - ectopic pregnancies are ipsilateral to the corpus luteum in 70-80% of cases 3, 5
- Endometrial thickness <8 mm excludes normal intrauterine pregnancy 1
- Endometrial thickness ≥25 mm virtually excludes ectopic pregnancy 1
- Describe intracavitary fluid rather than "pseudosac" to avoid clinical errors 5
Interpreting β-hCG Levels with Ultrasound
Critical β-hCG Thresholds
At β-hCG ≤3,000 mIU/mL in stable patients:
- Do not diagnose failed or ectopic pregnancy 1
- Obtain repeat ultrasound and β-hCG levels 1
- The gestational sac may not be visible until β-hCG reaches >3,000 mIU/mL 1
At β-hCG >3,000 mIU/mL:
- Absence of intrauterine pregnancy is strongly suggestive of ectopic pregnancy 1, 3, 6
- High-risk patients require prompt evaluation and treatment 6
At β-hCG >1,500 IU/L:
Serial β-hCG Monitoring
Obtain repeat β-hCG at least 2 days after initial presentation 1
- Viable intrauterine pregnancy: β-hCG increases approximately 50% in 48 hours in 99% of cases 1, 7
- Ectopic or failing pregnancy: slower rise or plateau 1
- Important caveat: 1% of viable intrauterine pregnancies have slower β-hCG rise and may be misdiagnosed 7
Pregnancy of Unknown Location (PUL)
When TVUS shows no intrauterine or ectopic pregnancy despite positive pregnancy test:
For β-hCG <1,000 mIU/mL:
- 21-40% risk of ectopic pregnancy 6
- Close follow-up with serial β-hCG and ultrasound 6
- TVUS sensitivity only 34.3% at β-hCG <2,000 mIU/mL 1
For β-hCG >2,000-3,000 mIU/mL:
Management approach:
- Repeat β-hCG every 48 hours until definitive diagnosis 4
- Serial ultrasound examinations 6
- Patient must be reliable for follow-up 4
Physical Examination Findings
While less specific than imaging, these findings increase likelihood of ectopic pregnancy:
- Cervical motion tenderness - LR+ 4.9 2
- Adnexal mass on palpation - LR+ 2.4 2
- Adnexal tenderness - LR+ 1.9 2
- Unilateral adnexal tenderness - often ipsilateral to corpus luteum 3
Critical Pitfalls to Avoid
Never use β-hCG value alone to exclude ectopic pregnancy with indeterminate ultrasound findings 3
Do not rely on risk factors - significant numbers of confirmed ectopic pregnancies occur without identifiable risk factors 4, 8
Avoid premature diagnosis at β-hCG ≤3,000 mIU/mL in stable patients - obtain serial measurements 1
Consider heterotopic pregnancy in fertility treatment patients - simultaneous intrauterine and ectopic pregnancy is rare but more common in this population 3, 6
Recognize atypical locations - interstitial, cervical, cesarean scar, ovarian, and abdominal pregnancies present differently 3
Immediate Surgical Referral Indications
Transfer immediately for surgery if: