Is breastfeeding safe for a mother with antiphospholipid syndrome who is on anticoagulation, and which anticoagulants (warfarin, low‑molecular‑weight heparin, unfractionated heparin, low‑dose aspirin, direct oral anticoagulants) are compatible?

Breastfeeding with Antiphospholipid Syndrome (APAS)

Breastfeeding is safe for mothers with antiphospholipid syndrome who require anticoagulation, and warfarin, unfractionated heparin (UFH), and low-molecular-weight heparin (LMWH) are all compatible and recommended first-line options. 1

Safe Anticoagulants During Breastfeeding

Strongly Recommended Options

Warfarin is the preferred oral anticoagulant for breastfeeding mothers with APAS requiring long-term anticoagulation:

• Warfarin is polar, nonlipophilic, and highly protein-bound, preventing excretion into breast milk 1
• Studies demonstrate no detectable warfarin in breast milk and no anticoagulant effect in breastfed infants 1
• The American Society of Hematology (ASH) provides a strong recommendation for warfarin use during breastfeeding 1
• Multiple observational studies have failed to identify any cases of infant bleeding in breastfed infants of mothers taking warfarin 1, 2

Unfractionated Heparin (UFH) is completely safe:

• UFH does not pass into breast milk due to its high molecular weight and strong negative charge 1
• The American College of Chest Physicians (ACCP) gives a Grade 1A recommendation for continuing UFH while breastfeeding 1

Low-Molecular-Weight Heparin (LMWH) is equally safe:

• Although small amounts of LMWH may be excreted into breast milk, oral bioavailability is extremely low 1
• A case series of 15 women showed either undetectable or very low anti-FXa levels in breast milk with no clinically relevant effect on nursing infants 1
• ACCP provides a Grade 1B recommendation for continuing LMWH during breastfeeding 1

Low-dose aspirin (< 100 mg/d) is acceptable:

• Low-dose aspirin was not associated with significant effects on neonatal platelet function in studies 1
• A prospective study of 15 breastfeeding mothers taking aspirin noted no negative effects 1

Alternative Agents (Use with Caution)

Acenocoumarol (commonly used in Europe):

• Has similar pharmacologic properties to warfarin and is considered safe 1

Danaparoid:

• Very low or no anti-Xa activity detected in breast milk 1
• Not absorbed by the GI tract after oral intake, making anticoagulant effect in infants unlikely 1
• ACCP gives a Grade 1B recommendation for continuing danaparoid while breastfeeding 1

Fondaparinux:

• Limited human data available; excreted in rat milk 1
• As a negatively charged oligosaccharide, significant absorption by nursing infants is unlikely 1
• ACCP suggests using alternative anticoagulants rather than fondaparinux (Grade 2C) 1

Contraindicated Agents

Direct oral anticoagulants (DOACs) must be avoided:

• ASH strongly recommends against using dabigatran, rivaroxaban, or apixaban in breastfeeding women 1
• ACCP recommends avoiding oral direct thrombin and anti-Xa inhibitors (Grade 1C during pregnancy, with manufacturers recommending against use during breastfeeding) 1
• No clinical data exist on effects in breastfed infants, and animal data show secretion into breast milk 1

Clinical Algorithm for APAS Mothers

Step 1: Determine Anticoagulation Need

• Women with thrombotic APAS require long-term anticoagulation 3, 4
• Women with obstetric APAS may require prophylactic anticoagulation postpartum 4, 5

Step 2: Select Appropriate Agent

For long-term anticoagulation:

• First choice: Warfarin (if patient can attend regular INR monitoring) 1, 2
• Alternative: LMWH or UFH (if warfarin monitoring is impractical or patient preference) 1

For short-term/prophylactic anticoagulation:

• First choice: LMWH or UFH 1
• Low-dose aspirin may be added if indicated 1

Step 3: Monitoring Considerations

• If using warfarin, perform regular INR monitoring to maintain therapeutic range 6, 7
• Note that lupus anticoagulant (LA) may interfere with INR determination in some APAS patients 7
• Consider coagulation testing and vitamin K status evaluation in the infant before initiating breastfeeding with warfarin 6

Important Caveats

Warfarin-specific considerations:

• While warfarin is safe, some breast-fed infants of mothers on warfarin have shown prolonged prothrombin times (though not as prolonged as mothers) 6
• Careful monitoring is warranted to ensure PT/INR values do not exceed recommended ranges 6
• The decision to breastfeed should involve careful consideration of available alternatives 6

Common pitfall to avoid:

• Do not assume that because a medication is safe during pregnancy, it is automatically safe during breastfeeding, or vice versa 1
• For example, warfarin is contraindicated during pregnancy but safe during breastfeeding 1

Premature infants:

• Effects of anticoagulants in premature infants have not been fully evaluated 6
• Extra caution and monitoring may be warranted in this population 6