Temporary increase in the risk for recurrence during pregnancy in women with a history of venous thromboembolism

There is strong evidence that the incidence of venous thromboembolism (VTE) is increased during pregnancy. However, it is unknown whether and to which extent pregnancy influences the risk for recurrent VTE in women with previous thrombosis. To investigate whether pregnancy temporarily increases the risk for recurrent thrombosis, we retrospectively evaluated the recurrence rate in 109 women who had at least one pregnancy after an episode of VTE by comparing the time period during pregnancy with the nonpregnant period. Forty-three women had a first recurrence during a total observation time of 1014 years. Eight events (73 observation years) occurred during pregnancy, and 35 events (941 observation years) occurred outside pregnancy. Recurrence rates per 100 patient-years were 10.9% during and 3.7% outside pregnancy. Relative risk during pregnancy was 3.5 (95% confidence interval, 1.6-7.8; P =.002). Our data suggest that pregnancy leads to a temporary increase in the risk for recurrent thrombotic events.