Efficacy of obstetric thromboprophylaxis and long-term risk of recurrence of venous thromboembolism

Abstract

Objective: To study the efficacy of thromboprophylaxis with low molecular weight heparin (LMWH) in pregnant women with one previous venous thromboembolic event (VTE). Secondary aims were to study the long-term risk of secondary recurrence, bleeding and obstetric complications.

Design: A prospective national study of long-term LMWH thromboprophylaxis in Sweden.

Settings: All hospitals in Sweden during January 1998-December 2002,

Participants: Pregnant women with one previous VTE and controls drawn from the Swedish Medical Birth Registry. The women were cross-matched with the Swedish Hospital Discharge Register to identify all recurrences and to ascertain the annual risk of recurrence.

Main outcome measures: Recurrence of VTE, bleeding complications at delivery and obstetric complications.

Results: 326 of 393 registered women could be evaluated. The relative risk reduction in VTE was 88%. There was an absolute increased risk of VTE during the thromboprophylaxis period: 1.2% compared to 0.2% among controls (p<0.001). The risk during the immediate post-treatment period (43-100 days post-partum) was increased 28-fold. The annual incidence of VTE after delivery was 1%. The risk of hematoma and major blood loss at delivery was increased during thromboprophylaxis (p<0.001). There were no differences in the incidences of preeclampsia, intrauterine growth restriction or placental abruption.

Conclusions: The relative risk reduction in VTE during thromboprophylaxis was 88%. After pregnancy, the annual long-term risk of recurrence was 1%. The risk was most pronounced in the post-treatment period. There was an increased risk of bleeding complications among women given LMWH, but there was no effect on obstetric complications.