Risk of pregnancy‐associated recurrent venous thromboembolism in women with a history of venous thrombosis

Background: Limited data exist on the risk of pregnancy‐associated venous thromboembolism (VTE) in women with a history of VTE. Objective: To evaluate the risk of recurrent pregnancy‐associated thrombosis in women with previous VTE in a large retrospective cohort study. Patients and methods: One hundred and fifty‐nine women with at least one pregnancy (293 pregnancies in total) after a VTE were included into the study. The patients underwent a standardized interview on their history of thrombosis and pregnancy‐associated complications. Results: Eight recurrent events occurred during 197 pregnancies without thrombosis prophylaxis. The probability of VTE during pregnancy without thrombosis prophylaxis was 6.2% (95% confidence interval 1.6–10.9%). The risk was constant over the whole period of pregnancy. Of the eight women with VTE during pregnancy four had heterozygous FV:R506Q, two in combination with hyperhomocysteinemia. No VTE occurred during 87 pregnancies with thrombosis prophylaxis. In the postpartum period 15 VTEs occurred, two of 83 (2.4%) after pregnancy termination, one of 53 (1.9%) after miscarriage, three of 10 (30%) after stillbirth and nine of 138 (6.5%) after live birth. Conclusions: Without thrombosis prophylaxis the risk for recurrent symptomatic VTE is substantial during the whole period of pregnancy in women with previous VTE. The majority of events occurred after delivery, reflecting the very high risk during the postpartum period. Prospective and comparative trials to ascertain efficacy and safety of prophylactic heparin are urgently needed.