Aims The excretion of low molecular weight heparin (LMWH) in breast milk was investigated in 15 lactating mothers after Caesarean section.
Methods Blood and milk samples were collected before and 3–4 h after once daily routine subcutaneous injection of 2500 IU dalteparin. Anti-Xa activity was measured by an assay utilizing prolonged clotting times in plasma or breast milk as an index of LMWH activity.
Results Plasma anti-Xa activities ranged from 0.074 to 0.308 IU ml−1 of plasma. Anti-Xa activities in breast milk ranged from < 0.005–0.037 IU ml−1 of milk. This is equivalent to a milk/plasma ratio of < 0.025–0.224.
Conclusions Therefore, it appears highly unlikely that puerperal thromboprophylaxis with LMWH has any clinically relevant effect on the nursing infant.