Postpartum venous thromboembolism: incidence and risk factors.

OBJECTIVE To calculate incidence of postpartum venous thromboembolism by week after delivery and to examine potential risk factors for venous thromboembolism overall and at different times during the postpartum period. METHODS A deidentified health care claims information database from employers, health plans, hospitals, and Medicaid programs across the United States was used to identify delivery hospitalizations among women aged 15-44 years during the years 2005-2011. International Classification of Diseases, 9th Revision, Clinical Modification diagnosis and procedure codes were used to identify instances of venous thromboembolism and associated characteristics and conditions among women with recent delivery. Incidence proportions of venous thromboembolism by week postpartum through week 12 were calculated per 10,000 deliveries. Logistic regression was used to calculate odds ratios for selected risk factors among women with postpartum venous thromboembolism and among women with venous thromboembolism during the early or later postpartum periods. RESULTS The incidence proportion of postpartum venous thromboembolism was highest during the first 3 weeks after delivery, dropping from nine per 10,000 during the first week to one per 10,000 at 4 weeks after delivery and decreasing steadily through the 12th week. Certain obstetric procedures and complications such as cesarean delivery, preeclampsia, hemorrhage, and postpartum infection conferred an increased risk for venous thromboembolism (odds ratios ranging from 1.3 to 6.4), which persisted over the 12-week period compared with women without these risk factors. CONCLUSION Risk for postpartum venous thromboembolism is highest during the first 3 weeks after delivery. Women with obstetric complications are at highest risk for postpartum venous thromboembolism, and this risk remains elevated throughout the first 12 weeks after delivery. LEVEL OF EVIDENCE II.