Ectopic pregnancy — single-dose methotrexate and the surgical choice (structured SAQ, 15 marks)

(a) Diagnosis, certainty and why the hCG cannot decide it (4 marks)

One mark for the diagnosis, one for the certainty level with justification, two for the hCG reasoning. ^[1]

• Diagnosis: a left tubal ectopic pregnancy, unruptured, with the woman currently haemodynamically stable.^[1]
• Certainty: high probability. An adnexal mass moving separately from the ovary with an empty gestational sac — the tubal ring or bagel sign — is a high-probability feature; it becomes diagnostic when a yolk sac, fetal pole or heartbeat is seen within it.^[1]
• No single hCG level locates a pregnancy. The hCG describes trophoblastic activity, not site. The discriminatory zone is a concept, not a rule: among pregnancies of unknown location with an hCG above 3000 IU/L, 39 of 358 women (about 11%) still had a viable intrauterine pregnancy.^[3]
• The diagnosis here was made by the ultrasound features, which is why treatment can proceed without further hCG sampling.

A candidate who writes "hCG above the discriminatory zone, therefore ectopic" loses the certainty mark and the reasoning mark, regardless of the eventual diagnosis. ^[3]

(b) Management options and selection (5 marks)

One mark for naming the options, one for the medical-versus-surgical reasoning, one for naming the dominant predictor of failure, one for the contraindications, one for an explicit plan. ^[1][2]

• Options: methotrexate (single-dose), laparoscopic salpingotomy, laparoscopic salpingectomy, or — not appropriate here — expectant management.^[1]
• Selection for this woman: single-dose methotrexate is appropriate because she is stable and unruptured, the mass is 2.6 cm, the hCG is moderate, and she has no stated contraindications. Because she has a single remaining tube, a tube-sparing approach is favoured where it is safe.^[1][2]
• Dominant predictor of methotrexate failure is a high presenting hCG, followed by fetal cardiac activity and larger mass size; in the Lipscomb series successfully treated women averaged 4019 mIU per millilitre against 13 420 in failures.^[5][4]
• Contraindications to exclude before methotrexate: renal or hepatic impairment, cytopenia, active peptic ulcer, pulmonary disease, breastfeeding, and inability to attend follow-up.^[1]
• Plan: baseline bloods including renal and liver function and full blood count, confirm no contraindication, consent including cytotoxic precautions, administer methotrexate, and book the day 4 and day 7 hCG.^[1]

If she were unstable, had a very high hCG with cardiac activity, or declined follow-up, the answer would be laparoscopic salpingotomy (tube-sparing) or salpingectomy. ^[1][6]

(c) The single-dose methotrexate protocol (4 marks)

One mark for the dose, one for the monitoring schedule, one for the day 4 to day 7 response rule, one for the failure action. ^[1][4]

• Dose: methotrexate 50 mg per metre squared by intramuscular injection, calculated from body surface area. Day of injection is day 1.^[4][8]
• Monitoring: serum hCG on days 1, 4 and 7, then weekly until the hCG is negative.^[1][8]
• Response rule: a fall of 15% or more between day 4 and day 7 indicates adequate response; continue weekly hCG to negative.^[1][7][8]
• Failure action: a fall of less than 15% between day 4 and day 7 requires clinical reassessment and usually a second dose, with a further hCG on day 7 after the second dose. Conversion to surgery is for methotrexate failure after repeat dosing, a rising hCG, new pain, or instability.^[1][8]

A transient rise between day 1 and day 4 is common and does not indicate failure — the decision point is day 4 to day 7. ^[1][4]

(d) Anti-D and counselling (2 marks)

One mark each. ^[1]

• Anti-D: she is RhD negative with a sensitising event; give anti-D after any surgical management and follow your local policy for medical management — noting that guideline positions differ by jurisdiction and the 2025 French guideline makes no ectopic-specific recommendation.^[1][10]
• Counselling: cytotoxic precautions and contraception with delaying attempts to conceive for 3 months — the guideline washout period, while the manufacturer advises 6 months — the symptoms to report (mouth ulcers, sore throat, dry cough, chest or abdominal pain, new or worsening pain), the mandatory follow-up to a negative hCG, and the written information and 24-hour contact number with explicit return criteria. Acknowledge the emotional impact and offer support.^[1][7][9]