Objectives To assess the use of low molecular weight heparin for the treatment of venous thromboembolism in pregnancy.
Design A prospective observational study.
Setting The maternity units in two university teaching hospitals and one district general teaching hospital.
Population Thirty-six consecutive women presenting with objectively diagnosed venous thromboembolism during pregnancy and the immediate puerperium.
Methods Treatment with the low molecular weight heparin enoxaparin, approximately 1 mg/kg sc, twice daily, based on early pregnancy weight.
Main outcome measures Peak anti-Xa activity (three hours post-injection), alterations in treatment, side effects and the use of regional anaesthesia.
Results In 33 women, the initial dose of enoxaparin provided satisfactory peak anti-Xa activity (median 0.8 u/mL, range 0.44–1.0 u/mL) and was continued. Three women required dose reduction since peak anti-Xa activities were above the therapeutic range (1.2, 1.2 and 1.1 u/mL). No woman developed thrombocytopaenia, haemorrhagic complication or further thromboembolic episode. Two women developed allergic skin reactions on enoxaparin and were changed to tinzaparin. Fifteen women had regional anaesthesia for delivery, with a reduced dose of enoxaparin (40 mg once daily), all without complication.
Conclusions Enoxaparin is a safe and effective treatment for venous thromboembolism during pregnancy and confers a major advantage over unfractionated heparin through its simplified regimen of administration.