[Thromboprophylaxis with low-molecular-weight heparin insufficient in high-risk pregnancy]

To evaluate the efficacy and safety of thromboprophylaxis with a low of low-molecular-weight heparin (LMWH) in women with an intermediate to high risk of pregnancy-related venous thromboembolism (VTE).

Retrospective cohort study.

We collected data from all pregnant women with an intermediate or high risk of VTE in the period 1996-2009. In accordance with protocol, pregnant women with an intermediate risk of VTE were treated with a prophylactic dose of LMWH for 6 weeks post partum, and pregnant women with a high risk were treated with a prophylactic dose of LMWH during the pregnancy and for 6 weeks post partum. Efficacy was defined as the incidence of VTE during pregnancy or < 3 months post partum, and safety as the incidence of post-partum haemorrhage (PPH) (> 500 ml blood loss) or severe PPH (> 1,000 ml blood loss).

We analysed 34 women (44 pregnancies) with an intermediate risk and 57 women (82 pregnancies) with a high risk of VTE. The incidence of pregnancy-related VTE despite thromboprophylaxis was 5.5% (95% CI: 2.4-12.3). All VTEs occurred in high-risk women, and risk was higher post partum than ante partum: 7.0% (95% CI: 2.9-16.7) and 1.8% (95% CI: 0.4-9.2%), respectively. The risk of PPH was 21.6% (95% CI: 14.3-31.3) and of severe PPH 9.1% (95% CI: 4.7-16.9) and was comparable in women who used LMWH during pregnancy and those who started LMWH post partum.

There was a considerable risk of pregnancy-related VTE in high-risk women despite a prophylactic dose of LMWH during pregnancy and in the post partum period. For these women thromboprophylaxis with a low, prophylactic dose of LMWH appeared to be insufficient.