The use of heparin in pregnant women with a history of venous thromboembolism is unwarranted, according to the results of a recent international study.
Researchers, led by Dr Patrick Brill-Edwards (McMaster university medical centre, Canada) prospectively studied 125 pregnant women with a single previous episode of venous thromboembolism. Heparin was withheld during pregnancy but anticoagulant therapy was given post partum (5,000 or 7,500U of unfractionated heparin given subcutaneously within 24 hours of delivery, followed by warfarin given for four to six weeks in doses adjusted to achieve a target international normalised ratio of 2.0 to 3.0).
Three of the 125 women (2.4 per cent) had a recurrence of venous thromboembolism during pregnancy. Two of these had antepartum deep-vein thrombosis (DVT) and the third suffered a pulmonary embolism. All three received low-molecular weight heparin for the remainder of their pregnancies. There were also three cases of postpartum DVT, for which all three women received subsequent anticoagulant therapy. One case occurred two weeks after warfarin prophylaxis had ceased. The other two cases occurred in women who had not received postpartum warfarin.
On entry into the study, blood was taken from 95 of the women and analysed for abnormalities. The three women who had experienced recurrence of venous thromboembolism were part of a sub-group of 51 women who had an abnormal laboratory result or a previous episode of idiopathic thrombosis or both. The researchers point out that there were no recurrences among the 44 women with normal laboratory results and a previous episode that was associated with a temporary risk factor.
The researchers conclude that the risk of recurrence of venous thromboembolism during pregnancy is low, and the routine use of heparin prophylaxis in women with a history of such events should be challenged (N Engl J Med 2000; 343:1439).