Postpartum blood transfusion and hemorrhage as independent risk factors for venous thromboembolism

Profuse postpartum hemorrhage (PPH) and red blood cell (RBC) transfusion have been suggested to be associated with venous thromboembolic events (VTE). However, it is not fully clear if they are independent major risk factors.

Women who gave birth in the Stockholm area between 1999 and 2002 were those studied, i.e., before the implementation of guidelines for thromboprophylaxis in pregnancy. In this population-based cohort study the Swedish Medical Birth Registry was linked to the National Discharge Registry and to the transfusion database. Cases with VTE were identified as well as the patient's transfusion history. The main outcome was an assessment of RBC transfusion and PPH as independent risk factors for postpartum thrombosis, analyzed in logistic regression models.

Out of the 82,376 deliveries, 56 cases of postpartum VTE were identified (0.7‰). Compared to the control group, the risk of VTE increased with the number of RBC transfusions: 1 to 3 units (OR = 3.3, 95% CI 1.2-8.9) and >3 units (OR = 5.2, 95%CI 1.7-16.1), but PPH was not found to be a major risk factor (OR = 1.4, 95% CI 0.5-3.5). Surprisingly, the small group treated with plasma in addition to RBC transfusion were not at a significantly increased risk (OR = 1.8, 95% CI 0.2-14.0). Preeclampsia and placental abruption were major risk factors.

We found RBC transfusion, but not PPH alone, to be an independent risk factor for postpartum VTE and propose that it should be included in the thromboprophylaxis algorithm for implementation during pregnancy.