Warfarin would be the most appropriate anticoagulation option for this patient. Warfarin is avoided during pregnancy because it crosses the placenta, causes fetal anticoagulation throughout the pregnancy, and is a teratogen. Because heparins do not cross the placenta and do not cause fetal anticoagulation, patients receiving chronic warfarin therapy are typically transitioned to either unfractionated or low-molecular-weight heparin (LMWH) during pregnancy. However, warfarin is not present in breast milk in any substantial amount and does not induce an anticoagulant effect in the breastfed infant. It is, therefore, a good option for anticoagulation in this patient. Similarly, heparins are minimally excreted in breast milk, and any drug ingested by an infant is unlikely to have any clinically relevant effect because of the very low bioavailability of oral heparins. Thus, LMWH and warfarin are both appropriate anticoagulant options for women who want to breastfeed.

It is unknown whether apixaban, dabigatran, or rivaroxaban are excreted in human milk. Therefore, known safe alternatives to these new oral anticoagulants should be used in women intending to breastfeed.

Fondaparinux has been demonstrated to be excreted in the milk of lactating rats. It is unknown whether it is excreted in human milk. Therefore, an alternative anticoagulant rather than fondaparinux is recommended for women who breastfeed.