Thromboprophylaxis with unmonitored intermediate-dose low molecular weight heparin in pregnancies with a previous arterial or venous thrombotic event

The comparatively high rate of complications, both to the mother and foetus, of warfarin and unfractionated heparin have led to an increased use of low molecular weight heparins (LMWH) in pregnant women at risk of thrombosis. However, despite reliable pharmacokinetics of LMWH, current practice is that anti-activated factor X levels are monitored in this group of patients. We report the use of unmonitored dalteparin in 27 pregnancies of 25 women who had previous thrombotic events. All women had normal renal function and weighed less than 85 kg prior to conceiving. The regimen consisted of 5000 IU dalteparin once daily started at the time of a positive pregnancy test, and increased to twice daily at 16-20 weeks gestation. In this cohort of patients there was a low complication rate. None of the women developed recurrent venous thromboses during these pregnancies but two women with known cerebral antiphospholipid syndrome developed recurrent cerebral ischaemia, which responded to an increase in dose.In our small group of patients, we have found that the use of intermediate-dose LMWH in pregnant women does not need to be monitored, and that it is safe and probably effective in preventing recurrent venous but not arterial thromboembolic events in high-risk pregnancies.