ARTICLE IN BRIEF
Investigators reported that the risk of thrombosis remains elevated beyond the traditional six-week postpartum period, and persists for at least 12 weeks after women give birth.
SAN DIEGO—The risk of blood clots, stroke, and heart attack in new mothers persists for at least three months after childbirth — but the elevated risk is still so uncommon that doctors are unsure if they even have to inform women to be vigilant about these events.
On the other hand, researchers here at the International Stroke Conference suggested that doctors ask new mothers about symptoms of blot clots such as swelling in the legs or more shortness of breath.
“While these events are rare, when they occur there can be serious consequences, including long-term disability and death,” said Hooman Kamel, MD, assistant professor of neurology and neuroscience at Weill Cornell Medical College in New York City.
“The risk of developing a clot is much higher than usual during the first six weeks after delivery,” he explained, “and we thought it was unlikely that the risk would suddenly return to normal at the end of six weeks, which is why we looked at what happens in the weeks following. It is important to know some women will continue to be at risk, and to search for ways that they can be effectively treated.”
Dr. Kamel noted that pregnancy increases the risk of blood clots, which can cause ischemic stroke, heart attacks, and venous thromboembolism. Thrombotic complications of pregnancy result in substantial morbidity and mortality, with a 5- to 30-percent mortality associated with postpartum stroke. Stroke accounts for 5–14 percent of all maternal deaths in developed countries, he said.
“Patients and providers should know that thrombotic risk remains higher than normal until 12 weeks postpartum,” Dr. Kamel said in a news briefing.
The study was funded by a grant from the National Institute of Neurological Disorders and Stroke, and was published in the Feb. 13 online edition of the New England Journal of Medicine simultaneously with its presentation at the meeting.
STUDY PROTOCOLS, DATA
Dr. Kamel and colleagues reviewed outcomes of women hospitalized for labor and delivery in California from 2005 to 2010. The study was limited to women having their first baby and excluded patients with a history of thrombosis prior to delivery. The researchers focused on the first delivery, because they reasoned that if acute thrombotic events occurred in the postpartum period with these women, they would be unlikely to go through subsequent pregnancies. The researchers relied on hospital diagnosis codes to determine if the woman had experienced the composite of ischemic stroke, acute myocardial infarction, or venous thromboembolism.
Dr. Kamel said that 1,015 women — of 1,687,930 women included in the study — experienced the composite endpoint events: 47 myocardial infarctions, 248 strokes, and 720 cases of venous thromboembolism.
They compared incidence of these events at six weeks postpartum; 12 weeks postpartum; 18 weeks postpartum; and at 24 weeks postpartum, and compared the risk for endpoint events a year later.
In the six-week period postpartum, 24.4 per 100,000 deliveries were associated with the composite endpoint events compared with 2.3 per 100,000 women in the year after delivery — an odds ratio of 10.8.
In the seven- to 12-week period, the rate of events was 5.6 per 100,000 deliveries compared with 2.6 per 100,000 women who were not pregnant in the same period a year later — an odds ratio of 2.2 — which was also significant, Dr. Kamel said. After 12 weeks, the risk of clots is not significantly higher than the usual risk in women who are not pregnant, he said.
Dr. Kamel said symptoms of these composite events include chest pain or pressure; difficulty breathing; swelling or pain in one leg; sudden severe headache; sudden change in consciousness, speech, vision, balance or strength or sensation on one side of the body.
Women at greatest risk for blood clots are those who have chronic high blood pressure, develop high blood pressure during pregnancy, are older, smoke, and have previously had blood clots. The researchers adjusted their study to concentrate on thrombotic risk due to pregnancy and not for other health conditions, Dr. Kamel said.
Lee Schwamm, MD, executive vice chairman of neurology at Massachusetts General Hospital and professor of neurology at Harvard Medical School, told Neurology Today: “The risk of these events are so low that I don't think it would be beneficial to tell new mothers, who have so many other things to be concerned about, that they have an elevated risk of stroke or heart attack.
“Most patients develop deep vein thrombosis before these other events of heart attack, stroke, and pulmonary embolism. So I would say be vigilant about a patient who calls in the first six weeks postpartum and complains about leg pain or swelling; she would be a patient you would want to prioritize for evaluating quickly,” he said.
Dr. Schwamm, who served as spokesperson for the American Heart Association/American Stroke Association (the sponsor of the conference), added: “This is clearly an area where you, as a physician, would want to intervene. Thromboembolism, while inconvenient, is not life threatening; but it can lead to other events such as pulmonary embolism, stroke, or heart attack.
“These people would clearly be treated with more than just aspirin,” Dr. Schwamm said. “They would get anticoagulation.
“Be aware that, although they are rare, serious thrombotic events can occur in the pregnancy and postpartum period. This study provides evidence that you just can't take out your handkerchief and wipe your brow once the baby comes out. You have to maintain that vigilance for a little bit longer.”
While current guidelines call for use of low-dose blood thinners in women at high-risk for stroke in the postpartum period, there are no recommendations for use of these medications in the general postpartum population.
Dr. Schwamm said such use might cause harm to women who are unlikely to need the medication. “Informing a patient of this risk might just create a false sense of alarm and might not be the most effective strategy,” he said. “A better strategy might be to make sure the general public is aware of the signs and symptoms of serious medical events, such as heart attack and stroke, and help young women understand that while it is a small risk, they too are at risk.
“I don't think there is general guidance as to how long the risk exists, and this is just one study in one population of patients that is giving us an idea about what that risk might be,” he said.