Thromboprophylaxis in pregnancy — structured SAQ (15 marks)

(a) Risk tier and antepartum plan (4 marks)

One mark per point. ^[1][2]

• High risk — a previous VTE is the single strongest risk factor and places her in the highest tier, compounded by obesity (BMI 32), smoking, and a family history (mother with PE).
• Antepartum prophylactic LMWH from the first trimester (e.g. enoxaparin, dose by weight).
• Consider thrombophilia testing given the strong family history, interpreting with caution in pregnancy (protein S falls); refer to haematology.
• Counsel on smoking cessation and the increased risk — smoking carries an adjusted odds ratio of around 2.96 for adverse outcome after reduced fetal movements and adds to VTE risk.

(b) Prophylactic LMWH dosing by weight and the dose evidence (4 marks)

One mark for the dose table, three for the evidence. ^[2][3]

• The Highlow trial (Bistervels, Lancet 2022): 1110 women with prior VTE randomised to intermediate-dose versus low-dose LMWH. No difference in VTE recurrence (2% versus 3%, RR 0.69, 95% CI 0.32 to 1.47) or major bleeding. Low-dose is the appropriate dose for prior VTE — do not use intermediate-dose.^[2]
• The Bruno trial (Obstet Gynecol 2022): weight-based enoxaparin (0.5 mg/kg twice daily) achieved prophylactic anti-Xa more reliably than fixed dose after caesarean (66% versus 44%, RR 1.49), especially in higher BMI.^[3]
• Prophylactic anti-Xa target range: 0.2 to 0.6 international units per mL, 4 hours post-dose at steady state.^[3]

(c) Labour, neuraxial anaesthesia, and postpartum plan (4 marks)

One mark per element. ^[1][2]

• Labour: plan the birth; hold the LMWH at the onset of labour or the morning of a planned delivery to allow neuraxial anaesthesia.
• Neuraxial anaesthesia timing: hold prophylactic LMWH for 10 to 12 hours before spinal or epidural (24 hours for a therapeutic dose), to avoid spinal haematoma.^[1]
• Postpartum: restart LMWH 6 to 12 hours after delivery once haemostasis is secure; continue for 6 weeks (high-risk tier).^[2]
• Plan the mode of delivery on obstetric grounds and arrange post-discharge support for injection technique and adherence.

(d) Maternal and fetal safety of LMWH (3 marks)

One mark per point. ^[1][5]

• LMWH does not cross the placenta (large molecular weight) and is not teratogenic — it is the preferred agent in pregnancy.^[5]
• LMWH is safe in breastfeeding — it is not excreted in breast milk in clinically relevant amounts.^[5]
• Maternal risks are low: bleeding (rare, but watch for wound haematoma and postpartum haemorrhage), heparin-induced thrombocytopenia (rare with LMWH), osteoporosis (rare with prophylactic courses), and allergic skin reactions. Where prolonged anticoagulation is needed postpartum, transition to warfarin (safe in lactation).^[1]