Anticoagulation in Pregnancy

Pregnancy and the first 6 weeks after delivery raise the risk of venous thromboembolism several fold. Low molecular weight heparin is the main drug because it does not cross the placenta, and warfarin and direct oral anticoagulants are avoided in most situations.

Drug safety. Warfarin crosses the placenta and causes embryopathy (weeks 6 to 12) and fetal bleeding. Direct oral anticoagulants cross the placenta and are not used. Heparins are safe in breastfeeding, as is warfarin.

• Treatment of venous thromboembolism: enoxaparin 1 mg/kg subcutaneously twice daily (or 1.5 mg/kg once daily), based on booking weight, continued through pregnancy and for at least 6 weeks after delivery, with a minimum total of 3 months.
• Prophylaxis (weight-banded): under 50 kg enoxaparin 20 mg daily; 50 to 90 kg 40 mg daily; 91 to 130 kg 60 mg daily; 131 to 170 kg 80 mg daily; over 170 kg 0.6 mg/kg daily. Higher doses (0.5 mg/kg twice daily) for body mass index 40 or over.
• Postpartum prophylaxis for 6 weeks: previous venous thromboembolism, high-risk thrombophilia, or 2 or more persisting risk factors. Intermediate risk: 10 days.
• Antiphospholipid syndrome with recurrent miscarriage: enoxaparin 40 mg daily with aspirin 75 mg daily; with thrombosis history: treatment-dose enoxaparin throughout.
• Heparin-induced thrombocytopenia: fondaparinux 2.5 mg daily or danaparoid, under specialist direction.
• Mechanical valves: warfarin at 5 mg or less daily, or twice-daily low molecular weight heparin, under specialist direction.

Delivery. Stop prophylactic enoxaparin at least 12 hours before neuraxial anaesthesia and therapeutic dose at least 24 hours before. Restart prophylactic dose 4 hours after catheter removal (at least 12 hours after the previous dose) and therapeutic dose 24 hours after delivery if bleeding is controlled.

Kidney impairment. Reduce the dose if creatinine clearance is under 30 mL/min, or use unfractionated heparin.

Weight change. Adjust weight-banded prophylaxis if weight changes by more than 10%, and adjust treatment doses by anti-Xa activity in extremes of weight or kidney disease (peak 0.6 to 1.0 units/mL for twice-daily dosing, 4 hours after the dose).

Thrombocytopenia. Reduce or stop heparin if platelets are under 50 x 10^9/L, with haematology advice.

Special groups. Breastfeeding women can take heparins and warfarin; avoid direct oral anticoagulants. Adolescent mothers and those with preeclampsia, caesarean delivery, postpartum haemorrhage, infection or immobility need risk review. In East Africa, postpartum haemorrhage risk and limited laboratory monitoring shape the balance, and unfractionated heparin may be the only available option.

Monitoring. Check a full blood count at baseline and every 3 to 4 weeks, and creatinine at baseline. Teach the patient to stop injections and attend at the onset of labour, bleeding or leaking fluid.

Referral and escalation. Seek obstetric and haematology review for a previous clot, thrombophilia, antiphospholipid syndrome, mechanical valves and any bleeding.

Stopping. Stop treatment 6 weeks after delivery (at least 3 months in total), and prophylaxis as planned.