Summary
Venous thromboembolic disease remains the commonest cause of maternal death. The management
of thromboprophylaxis in high risk women during pregnancy is contentious. Low molecular
weight heparins (LMW) have theoretical advantages compared with unfractionated heparin
and warfarin but have been poorly studied in pregnancy. We report on the use of LMW
heparin (Fragmin) as thromboprophylaxis in thirty four high risk pregnancies.
All the women had a previous thrombosis or a thrombosis in their current pregnancy
+/- a recognised thrombophilic state (eleven had the antiphospholipid syndrome).
Fragmin was given subcutaneously to maintain trough anti-Xa activity of 0.15-0.2 U/ml
and 2 h post injection levels of 0.4-0.6 U/ml. The levels were checked monthly during
pregnancy. Most women required 5,000U Fragmin once daily during the first trimester
unless they were greater than 100 kg at the start of pregnancy. The mean time for
dosage increase was 20.5 week (S.D. 8.2). 26/34 pregnancies (76%) required twice daily
at the end of pregnancy. Epidural anaesthesia was managed by omitting Fragmin dose
or inserting the needle 6 hours after the previous Fragmin injection. There were no
thromboembolic events, thrombocytopenias or excessive haemorrhage. One woman had osteoporotic
vertebral collapse post partum, she had no other risk factors for osteoporosis.
LWM heparin (Fragmin) appears to be efficacious in preventing recurrent thromboembolic
disease in pregnant women at high risk, but it is notable that osteoporotic fractures
occurred post partum in one woman. Further trials are required to determine optimal
dosage and safety.
