Women may be at risk for thrombotic events for up to 12 weeks after delivering a baby, twice as long as previously thought, according to a study published online Feb. 13 in The New England Journal of Medicine. The findings were simultaneously presented at the International Stroke Conference in San Diego.

“Pregnancy increases the risk of thrombotic events. These events are very rare, but when they happen, it’s very traumatic for the patients, their families and for the physicians taking care of them. When an event occurs in someone at that age, it’s very difficult, so that’s what led us to look at this topic,” lead author Hooman Kamel, MD, of Weill Cornell Medical College in New York, told Cardiovascular Business.

Kamel explained that the postpartum period is conventionally believed to be six weeks, but he and his co-investigators hypothesized that the risk for a thrombotic event would be higher than normal beyond six weeks.

“The risk is so much higher during those six weeks that we thought it would be unlikely for it to return to normal so soon after that,” he said.

They analyzed discharge data from women who gave birth in California hospitals between 2005 and 2010. They identified women diagnosed with either an ischemic stroke, acute MI or venous thromboembolism and determined the likelihood of a first thrombotic event during sequential six-week time periods and compared them to the same time frame one year later.

There were 1,015 thrombotic events among the 1,687,930 women in the study during the one year and up to 24 weeks postpartum. The risk of primary thrombotic events was especially high during the six-week postpartum period compared with the same time period one year later (411 events vs. 38 events, amounting to an odds ratio [OR] of 10.8).

Risk was also higher during the seven- to 12-week postpartum period compared with the same period one year later (OR 2.2). After 12 weeks, the risk of a thrombotic event was not significantly higher.

Kamel said their findings suggest avenues for future research. One possible avenue is to evaluate the risks and benefits of extending prophylactic use of blood thinners in high-risk women beyond six weeks after delivery.

“One implication applies to all patients,” he added. “Clinicians and patients should be aware of the symptoms of thrombotic events and understand they are at higher risk than usual for 12 weeks after labor and delivery.”