Figure 1.
VTE recurrence risk and duration of anticoagulation. For men and nonpregnant women with an index VTE event, VTE recurrence risk is driven by risk factors that were present at the time of the initial VTE event.1,2 The predicted annual recurrence risk after an unprovoked VTE event is higher than that after a VTE provoked by a major transient risk factor. VTE occurring in the context of minor risk factors are associated with higher predicted recurrence risk than those occurring in the context of major transient risk factors.6 Recurrence risks for patients with major persistent risk factors (most notably active cancer) are among the highest of all.1,2 Guideline recommendations on duration of anticoagulation are guided by data including VTE recurrence risk and bleeding risk on anticoagulation, with limited and indefinite duration anticoagulation being recommended for patients with low and high recurrence risks respectively.2,43 For some patients including “cis” and transgender women whose VTE occurred in the context of hormone use, estimation of recurrence risk may be particularly challenging because of knowledge gaps, and these areas are important research priorities.27 For pregnant women with prior VTE (especially those with an unprovoked or a hormone-provoked VTE,21 predicted recurrence risk during pregnancy is sufficiently high to warrant both antenatal and postnatal thromboprophylaxis, whereas postpartum thromboprophylaxis only is recommended for women with lower predicted recurrence risks.25 The optimal LMWH dose for women with prior VTE is currently being investigated in the ongoing Highlow study (NCT 01828697; highlowstudy.org).