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Blood Clot Risk Lingers in New Mothers

March 06, 2014

Postpartum women are at increased risk of blood clots for twice as long as previously believed, according to new research, which stopped short of suggesting the use of prophylactic anticoagulant therapy in high-risk patients continue beyond the recommended 6 weeks after delivery.

New mothers are as much as 22 times more likely to suffer venous thromboembolism than the general population of women, noted the study. To assess whether that likelihood extended past the conventional 6-week risk window, the study’s authors reviewed the hospital records of approximately 1.7 million Californian women aged 12 years or older who delivered between Jan. 1, 2005 and June 30, 2010. They compared incidences of thrombosis during the first 41 days after delivery to the same period exactly 1 year later to ensure thrombotic risk was due to pregnancy and not another health condition. They then repeated the same analysis for postpartum days 42 through 83, 84 through 125, and 126 through 167.

Thrombosis occurred in 22 out of 100,000 women within 6 weeks of delivery compared with 3 women across the same number of deliveries from 7 to 12 weeks, noted the researchers, who said the absolute increase in risk of thrombosis beyond 6 weeks was small, but still significant. Notably, they discovered risks were no longer heighted after 12 weeks of delivery.

“Although uncommon, postpartum thrombotic events are some of the most serious complications of pregnancy,” said lead study lead author Dr. Hooman Kamel, an assistant professor of neurology and neuroscience at Weill Cornell Medical College and a neurologist at New York-Presbyterian Hospital. “Postpartum stroke alone accounts for approximately 10% of all maternal deaths in developed countries.”

Current guidelines call for the use of low-dose, preventive blood thinners in at-risk women for 6 weeks after delivering, according to Dr. Kamel, who said additional research should compare the outcome of postpartum use of blood-thinning therapy in these high-risk patients for 6 versus 12 weeks to determine whether the treatment should last longer.

He noted that all providers who interact with postpartum patients should be aware of the possible symptoms of thrombosis — chest pain and neurological defects, for example — and realize these patients remain at heightened risk of thrombotic complications until at least 12 weeks after delivery.

“For pharmacists especially, this knowledge may be helpful when discussing the risk-benefit and timing of postpartum contraception, since oral contraception has been associated with an increased risk of thrombotic events,” he added.

The article was published online in the New England Journal of Medicine.


—Dan Cook



1. Kamel H, Navi BB, Sirram N, Hovsepian DA, Devereux RB, Elkind MSV. Risk of a thrombotic event after the 6-week postpartum period. N Engl J Med. 2014 Feb 13. [Epub ahead of print]

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