Accumulation of low molecular mass heparin during prophylactic treatment in pregnancy

A history of thromboembolism is associated with an increased risk of new th romboembolic events during pregnancy. Prophylaxis with heparin during pregn ancy implicates long-term treatment with daily injections with either unfra ctionated heparin (UFH) or low molecular mass heparin (LMMH). Prolonged tre atment with heparin may result in endothelial absorption and drug accumulat ion. In order to test this hypothesis, anti-FXa activity during pregnancy w as measured in four women allergic to conventional UFH, who were treated wi th LMMH (dalteparin; Pharmacia). It was found that, at the commencement of treatment, it took more than 8 days to reach a steady maximum peak value, l ocated 3 h after the given dose. One daily dosage of 5000 IU anti-Xa result ed in a measurable level of FXa for 24 h in pregnancy week 40, compared wit h 17 h at pregnancy week 37. The implications of an elevated anti-FXa activ ity during pregnancy, especially during the third trimester and at partus, are discussed. We present a reduced dose regime near term and during delive ry. (C) 2001 Lippincott Williams & Wilkins.