A 30-year-old woman with a confirmed left ampullary ectopic pregnancy at 7 weeks has a β-hCG of 2200 mIU/mL. She is haemodynamically stable with no haemoperitoneum. She meets criteria for methotrexate (MTX) therapy. She receives single-dose MTX 50 mg/m². On day 7, her β-hCG has fallen from 2200 to 1800 mIU/mL (18% decline). What is the correct interpretation and next step?
- A Successful treatment — continue weekly monitoring until β-hCG < 5 mIU/mL
- B Treatment failure — proceed to immediate surgical management
- C Insufficient decline — administer second dose of MTX and reassess on day 14 ✓
- D Day 4 to Day 7 β-hCG must decline by ≥ 15%; an 18% decline means success
Explanation
Single-dose MTX protocol requires a ≥ 15% decline in β-hCG between Day 4 and Day 7 (not from baseline to Day 7) for treatment success. After the initial expected transient rise on Day 1–4 (due to ongoing trophoblastic activity), the Day 4–Day 7 decline must be ≥ 15%. An 18% decline from the initial value (Day 0 to Day 7) does not reflect the correct comparison; if the Day 4 value was, for example, 2500 and Day 7 is 1800, that is a 28% decline (adequate). Without the Day 4 value, a decline from 2200 to 1800 (18%) from Day 0 to Day 7 that is < 15% of Day 4 value mandates a second MTX dose. Per ACR/ACOG guidelines, if Day 4–7 decline < 15%, a second dose is administered and Day 11–14 values are checked.
Reference: Williams Obstetrics, 26th ed.
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Written and medically reviewed by the StethoPrep medical team.