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How long does increased blood clot risk persist after delivery?

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The initial period after delivery, known as the postpartum period, is associated with an increased risk of a deep vein thrombosis (DVT; blood clot). The clot typically forms in the calf and if it becomes dislodged it can travel to the lung and cause a pulmonary embolus, which may be fatal. A new study was conducted to determine how long that heightened risk is present and to what degree. The findings were published on April 3 in The New England Journal of Medicine by researchers at Columbia University and Cornell Medical College, both in New York.

The researchers note that the postpartum period is associated with a significantly increased risk of a DVT; however, it is uncertain to what degree this increased risk persists beyond the conventionally defined six week postpartum period. They reviewed claims data of 1,687,930 women with their first delivery who were discharged from nonfederal emergency departments and acute care hospitals in California. The records comprised all women who were hospitalized for labor and delivery between January 1, 2005, and June 30, 2010. The reviewed validated diagnosis codes to identify complications including stroke, acute myocardial infarction (heart attack), or venous thromboembolism. They then conducted a statistical analysis to determine each patient's likelihood of a first thrombotic event during sequential six week periods after delivery. This risk was compared to the corresponding 6-week period one year later.

The investigators found that 1,015 had a thrombotic event (248 cases of stroke; 47 cases of myocardial infarction; and 720 cases of venous thromboembolism) in the period of one year plus up to 24 weeks after delivery. The risk of primary thrombotic events was significantly higher within six weeks after delivery than in the same period one year later (411 events vs. 38 events; absolute risk difference: 22.1 events) per 100,000 deliveries and 10.8-fold increased risk. The researchers also found a small but significant increase in risk during the period of seven to 12 weeks after delivery, compared to the same period one year later (95 vs. 44 events; absolute risk difference: 3.0 events) per 100,000 deliveries and a 2.2-fold increased risk. Beyond the first 12 weeks postpartum, no significant increased risk was found.

The authors concluded that an increased risk of thrombosis persisted until at least 12 weeks after delivery. However, the absolute increase in risk beyond six weeks postpartum was low.

Take home message:

This study notes that a woman must be vigilant of a DVT particularly during the first 12 weeks postpartum. Deep vein thrombosis occurs without symptoms about 50% of the time. When symptoms do occur, they may include: swelling in the leg; red, discolored, or white skin; rapid heartbeat (tachycardia); slight fever; warm skin; more visible surface veins; or dull ache, tightness, tenderness or pain in the leg (these symptoms may only occur while walking or standing).

The risk of a DVT can be decreased by avoiding sedentary periods, particularly sitting with your legs crossed. After delivery, many women may be less active because of episiotomy discomfort, a cesarean section, or fatigue; however, it is important to maintain a level of activity. Preventing a DVT caused by long periods of sitting or reclining involves moving the lower leg. Flexing (bending) the knees may be helpful when sitting, and avoid prolonged periods of sitting. Wear loose clothing, avoid alcohol, and drink plenty of fluids (this is also necessary to maintain hydration if breastfeeding).