Using administrative claims data, the authors of a new study published in NEJM found significantly increased risks for primary thrombotic events beyond the 6-week postpartum period, when the risk is well recognized to be high. However, absolute increases in risk from 7 to 12 weeks after delivery were small.
Pregnancy significantly increases the risk of thrombosis. This heightened thrombotic risk rises further during the postpartum period, which is conventionally defined as the 6 weeks after delivery.
• What is known about the prothrombotic state of the postpartum period and what are current recommendations for women at high risk for venous thromboembolism?
As compared with the nonpregnant state, the 6-week postpartum period is associated with increases by a factor of 3 to 9 in the risk of stroke, by a factor of 3 to 6 in the risk of myocardial infarction, and by a factor of 9 to 22 in the risk of venous thromboembolism. It is unknown whether these risks remain increased after the conventionally defined 6-week postpartum period. Guidelines for the treatment of thrombotic disorders during pregnancy advise the discontinuation of prophylactic therapy at 6 weeks after delivery in women at high risk for venous thromboembolism.
• In this study, what was the odds ratio of having a thrombotic event within 6 weeks after delivery compared to the same period one year later?
Significantly more thrombotic events occurred within 6 weeks after delivery than during the same period 1 year later (411 events, or 24.4 events per 100,000 deliveries, vs. 38 events, or 2.3 events per 100,000 deliveries), corresponding to an absolute risk difference of 22.1 (95% confidence interval [CI], 19.6 to 24.6) per 100,000 deliveries and an odds ratio of 10.8 (95% CI, 7.8 to 15.1).
Morning Report Questions
Q: What did this study demonstrate with respect to thrombotic risk in women after the 6-week postpartum period?
A: In the period of 7 to 12 weeks after delivery, there was a modest but still significant increase in the number of thrombotic events, as compared with the same period 1 year later (95 events, or 5.6 events per 100,000 deliveries, vs. 44 events, or 2.6 events per 100,000 deliveries), corresponding to an absolute risk difference of 3.0 (95% CI, 1.6 to 4.5) per 100,000 deliveries and an odds ratio of 2.2 (95% CI, 1.5 to 3.1). The risk was no longer significantly elevated after 12 weeks, with an odds ratio of 1.4 (95% CI, 0.9 to 2.1) for the period of 13 to 18 weeks after delivery and an odds ratio of 1.0 (95% CI, 0.7 to 1.4) for the period of 19 to 24 weeks after delivery. In post hoc exploratory analyses, the thrombotic risk was increased during the period of 13 to 15 weeks after delivery (odds ratio, 2.0; 95% CI, 1.1 to 3.6) but was no longer elevated in the period of 16 to 18 weeks (odds ratio, 1.0; 95% CI, 0.6 to 1.8).
Q: What characteristics of patients were associated with a higher risk of postpartum thrombosis?
A: As compared with patients without postpartum thrombosis, those with postpartum thrombotic events were older, were more likely to be white or black than Hispanic or Asian, were less often privately insured, and were more likely to have risk factors for thrombosis. There was also a significantly higher risk within 6 weeks after delivery among women who had undergone cesarean section than among those who had undergone vaginal delivery.