A woman with a rising β-hCG of 3200 mIU/mL and no intrauterine gestational sac on transvaginal ultrasound is found to have an adnexal mass of 2.5 cm. She is haemodynamically stable, has no contraindications, and is eligible for methotrexate treatment. According to the single-dose methotrexate protocol, what constitutes treatment success?
- A β-hCG level falls by any amount between Day 1 and Day 4
- B β-hCG falls by ≥15% between Day 4 and Day 7; if not, a second dose is given ✓
- C β-hCG becomes undetectable (<5 mIU/mL) by Day 7
- D Adnexal mass resolves completely on Day 7 ultrasound
Correct answer: B. β-hCG falls by ≥15% between Day 4 and Day 7; if not, a second dose is given
Explanation
In the single-dose methotrexate protocol for ectopic pregnancy, β-hCG is measured on Day 1 (day of injection) and Day 4 and Day 7. A transient rise in β-hCG between Day 1 and Day 4 is expected (due to cytotoxic cellular death releasing β-hCG) and does not indicate treatment failure. Treatment success is defined as a ≥15% decline in β-hCG between Day 4 and Day 7. If this criterion is not met, a second dose is given. β-hCG should be followed weekly until undetectable; adnexal mass resolution lags behind β-hCG fall and is not used to define success.
Reference: Williams Obstetrics, 26th ed.
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Written and medically reviewed by the StethoPrep medical team.