Thromboprophylaxis in pregnancy — structured oral station (12 minutes)

Opening prompt — "Risk-tier this woman and tell me your antepartum plan."

Model response: ^[1][2]

• "She is high risk. A previous pulmonary embolism is the single strongest risk factor, compounded by her BMI of 35 and her age. The ASH 2018 and ACOG PB 196 guidelines put her firmly in the high-risk tier."
• "My antepartum plan is prophylactic low-molecular-weight heparin from the first trimester — enoxaparin, dose by weight. Given her BMI of 35, that is 40 mg daily in the standard tier, with consideration of anti-Xa monitoring if she gains significant weight."
• "I would also arrange a haematology review and consider thrombophilia testing given the prior PE, interpreting with caution in pregnancy."

Probe 1 — "Defend the dose with the evidence."

• "The Highlow trial (Bistervels, Lancet 2022) randomised 1110 women with prior VTE to intermediate-dose versus low-dose LMWH for antepartum plus 6 weeks postpartum. There was no difference in VTE recurrence — 2% versus 3%, relative risk 0.69, 95% CI 0.32 to 1.47 — and no difference in major bleeding. The conclusion was that low-dose is the appropriate dose."^[2]
• "So I would use prophylactic, not intermediate, dosing. Over-treating does not help and adds bleeding risk."^[2]

Probe 2 — "What about her weight? Bruno showed something about that."

• "Yes. The Bruno trial (Obstet Gynecol 2022) looked at post-caesarean prophylaxis in fixed-dose versus weight-based enoxaparin. Weight-based — 0.5 mg per kg twice daily — achieved prophylactic anti-Xa levels more reliably than fixed dose, 66% versus 44%, RR 1.49. The benefit was greatest in higher BMI."^[3]
• "For a woman at her BMI, if she has a caesarean, I would favour weight-based dosing or at least 40 mg twice daily, with anti-Xa monitoring if there is uncertainty."^[3]

Probe 3 — "She goes into labour and wants an epidural. What do you do about the LMWH?"

• "I would hold the prophylactic LMWH for 10 to 12 hours before neuraxial anaesthesia, to avoid spinal haematoma. A therapeutic dose would need 24 hours."^[1]
• "I would coordinate with the anaesthetist around the planned delivery, and restart the LMWH 6 to 12 hours after the epidural is removed or after delivery once haemostasis is secure."^[1]

Probe 4 — "What is your postpartum plan?"

• "Continue the LMWH for 6 weeks postpartum — she is high risk. That is the duration the Highlow trial used and what the guidelines recommend for prior VTE."^[2]
• "If she has a caesarean, weight-based enoxaparin postpartum with anti-Xa monitoring given her BMI. I would arrange community support for injection technique."^[3]
• "I would counsel her that LMWH is safe in breastfeeding, and that we can transition to warfarin postpartum if a longer course is needed — warfarin is safe in lactation, though contraindicated in pregnancy."^[5]

Probe 5 — "She asks whether the injections will harm the baby. Talk me through your counselling."

Communication is a scored domain. ^[1]

• "These injections do not cross the placenta and do not harm the baby — they are the safest blood-thinning option in pregnancy. They do not cause birth defects and are safe in breastfeeding too."
• "The reason we use them is that pregnancy makes your blood more likely to clot, and because you have had a clot before, the risk is higher. The injections bring the risk right down."
• "I would teach you how to give them, and arrange follow-up to make sure everything is going smoothly."