Summary

It is not known whether women who develop venous thromboembolism (VTE) during pregnancy have a higher or lower incidence of recurrentVTE than women with unprovokedVTE.The aim of the study was to compare the risk of recurrent VTE among women with pregnancy-associated VTE to women with unprovoked VTE. Hospital discharge data identified women age 18–46 years old with pregnancy-associated or unprovoked index VTE between 1994 and 2005. Risk of recurrent VTE was compared between six and 60 months after the index event using both age-matched comparison of disease-free survival and proportional hazard modelling, adjusting for age and other risk factors. The Kaplan-Meier incidence of recurrent VTE in 1085 women with pregnancy-associated VTE was 5.8% versus 10.4% in 7625 women with unprovoked VTE (p=0.02). Twelve of 34 (35%) recurrent events in the pregnancy-associated group occurred during a subsequent pregnancy compared with 29 of 331 (8.7%) events in the unprovoked group (p<0.001).In the risk-adjusted multivariate model, women with pregnancy-associated VTE had a significantly lower risk of recurrent VTE (HR = 0.6, 95%CI=0.4–0.9). Overall, the incidence of recurrentVTE during subsequent pregnancies was higher in the pregnancy group, 21 of 465 (4.5%), than in the unprovoked group, 37 of 1353 (2.7%, RR=1.7, CI:1.0–2.8). Compared to women with unprovoked VTE, women with pregnancy-associated VTE had a significantly lower long-term risk of recurrentVTE but a higher risk of recurrent VTE during a subsequent pregnancy.These findings should be considered when decisions are made about VTE prophylaxis in women with a history of pregnancy-associated VTE.