Risk of a Thrombotic Event After the 6-Week Postpartum Period

Study Questions:

What is the duration of heightened risk for thrombosis in the post-partum period?

Methods:

This was a retrospective crossover-cohort study. Eligible patients were women who had been hospitalized for labor and delivery between January 2005 and June 2010; the authors used administrative claims data on all discharges from nonfederal emergency departments and acute care hospitals in California. The authors compared each patient’s likelihood of a first thrombotic event (a composite of ischemic stroke, acute myocardial infarction, or venous thromboembolism) during sequential 6-week periods after delivery with the likelihood of an event during the corresponding 6-week period 1 year later.

Results:

Among 1,687,930 women with a first recorded delivery, 1,015 women experienced a thrombotic event (248 cases of stroke, 47 cases of myocardial infarction, and 720 cases of venous thromboembolism) in the 1 year plus 24 weeks after delivery. The risk of a thrombotic event was markedly higher 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), with an absolute risk difference of 22.1 (95% confidence interval [CI], 19.6-24.6) per 100,000 deliveries and an odds ratio of 10.8 (95% CI, 7.8-15.1). Compared to the same period 1 year later, there was a modest, but still significant increase in the number of thrombotic events within 7-12 weeks after delivery (95 events, or 5.6 events per 100,000 deliveries vs. 44 events, or 5.6 events per 100,000 deliveries), with an absolute risk difference of 3.0 (95% CI, 1.6-4.5) per 100,000 deliveries and an odds ratio of 2.2 (95% CI, 1.5-3.1). After 12 weeks, the risk was no longer significantly elevated.

Conclusions:

Although the risk for a primary thrombotic event in the postpartum period is highest in the 6 weeks after delivery, the elevated risk persists up until 12 weeks following delivery.

Perspective:

Although limited by the lack of prospective case ascertainment (as acknowledged by the authors), this study is an important contribution that may help inform guidelines about the duration of prophylactic anticoagulation in high-risk patients postpartum. As the risk for a primary thrombotic event is elevated to at least 12 weeks postpartum in this study, consideration should be given to extension of therapy to this time period.

Clinical Topics: Pulmonary Hypertension and Venous Thromboembolism, Vascular Medicine

Keywords: Blood Coagulation, Myocardial Infarction, Stroke, California, Venous Thromboembolism, Postpartum Period, Risk Factors, Emergency Service, Hospital, Delivery, Obstetric


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