Source: Kamel H, et al. Risk of a thrombotic event after the 6-week postpartum period. N Engl J Med 2014; Feb 13. Online DOI: 10.1056/NEJMoa1311485.
Even in healthy women, the postpartum period is linked with a multitude of thromboembolic events like ischemic stroke. As during pregnancy, intrinsic clotting factors increase until delivery and then gradually decrease back to normal around six weeks postpartum. It is thought that an increased risk of thromboembolism is expected until the clotting factors returned to normal. Despite this belief, there is little evidence to actually confirm or dispute this hypothesis.
Attempting to expand on the meager evidence base, Kamel et al sampled nonfederal emergency departments and acute care facilities in California to select women who were hospitalized to undergo labor between the years of 2005 and 2010. Using a claims database that stored all of the information, the authors compiled a data set of the primary outcomes of ischemic stroke, acute myocardial infarction and venous thromboembolism. They proceeded to compare rates of thrombotic events during the six weeks following delivery with a corresponding 6-week period one year later, performing a logistic regression to assess event likelihood.
Kamel et al used a claims database on all discharges from nonfederal emergency departments and acute care hospitals in California, and identified women who were hospitalized for labor and delivery between Jan. 1, 2005, and June 30, 2010. In addition, they tabulated a composite primary outcome of ischemic stroke, acute myocardial infarction, or venous thromboembolism in those same women. They then used logistic regression to assess each patient's likelihood of a first thrombotic event during sequential 6-week periods after delivery, as compared with the corresponding 6-week period one year later.
Of the 1,687,930 women who successfully delivered, 1,015 had a thrombotic event of some sort (47 had a myocardial infarction, 248 had a stroke, and 720 had a venous thromboembolism) in the period of one and a half years following delivery. Thrombotic events were much more common in the six weeks after pregnancy than they were in the corresponding 6 weeks a year later. To a lesser but still significant degree, the same was true of the period of 7-12 weeks after delivery, where thrombotic events were again more likely than the corresponding period a year after. Beyond the first 12 weeks there were no significant differences in thrombotic event risk. In order to further understand the mechanisms of postpartum thrombotic risks and develop preventative measures minimizing these risks, more prospective study is required.