Postpartum VTE Risk Highest Soon After Birth

Norra MacReady

April 07, 2014

A woman's risk for postpartum venous thromboembolism (VTE) is highest in the first few weeks after delivery and then drops steadily through week 12, a new study suggests. Pregnancy complications increase the risk for postpartum VTE.

The study is one of the few to track the incidence of postpartum VTE on a weekly basis, lead author Naomi K. Tepper, MD, MPH, from the Prevention and Health Promotion and the Division of Blood Disorders, National Center on Birth Defects and Developmental Disabilities, Centers for Disease Control and Prevention, Atlanta, Georgia, and colleagues write in the May issue of Obstetrics and Gynecology.

It is well established that the risk for VTE rises shortly after birth, largely because of pregnancy-related hypercoagulability. However, most previous studies report an aggregate risk for a given time, rather than week-by-week. Different components of the clotting system return to normal at different times, ranging from immediately after delivery to 6 to 12 weeks later, and little is known about how these changes affect VTE risk.

Knowledge is also scarce about the effect of risk factors on VTE risk over time. "More precise information about weekly incidence and risk factors might allow for more informed decisions regarding postpartum prophylaxis or initiation of certain medications that may pose additional risk for venous thromboembolism such as estrogen-containing contraceptives," the authors write.

The researchers obtained deidentified information on women aged 15 to 44 years from the Truven Health MarketScan Commercial and Multi-State Medicaid databases, which contain healthcare claims information from employers, hospitals, health plans, and Medicaid programs across the United States. The analysis covered 2005 through 2011. For women having multiple deliveries during those years, the researchers only included data from the first delivery. The women were followed-up from day 0, defined as the date of first report of delivery diagnosis or procedures, through postpartum week 12. Enrollment ended on September 30, 2011, to ensure all participants could be followed-up for 12 weeks. The investigators identified VTE events identified through the International Classification of Diseases, 9th Revision, Clinical Modification, for deep venous thrombosis (DVT) and pulmonary embolism (PE).

They excluded patients with hydatidiform mole, ectopic pregnancy, or other abnormal products of conception from the study. The final analysis included 1,540,026 deliveries in the private insurance database and 1,002,536 in the Medicaid database.

From 2005 to 2011, there were 2456 VTEs during the first 12 postpartum weeks among women with private insurance and 1713 among women in the Medicaid database. The overall VTE incidence per 10,000 deliveries was 15.95 (95% confidence interval [CI], 15.33 - 16.59) and 17.09 (95% CI, 16.30 - 17.91), respectively.

The number of VTEs in both groups was highest during week 1: There were 1417 VTEs in the private insurance group and 943 in the Medicaid group, for an incidence of 9.20 per 10,000 deliveries (95% CI, 8.73 - 9.69) and 9.41 (95% CI, 8.82 - 10.03), respectively. By week 2, the incidence had already dropped off considerably, to 372 VTEs and 259 VTEs, for a respective incidence of 2.42 (95% CI, 2.18 - 2.67) and 2.58 (95% CI, 2.29 - 2.92) in the first week compared with the second week.

Those rates continued to decline, and by week 12, there were 20 VTEs in the private insurance group and 17 in the Medicaid group, for an incidence of 0.13 (95% CI, 0.08 - 0.20) and 0.17 (95% CI, 0.11 - 0.27), respectively.

Severe postpartum complications, such as heart failure, pulmonary edema, adult respiratory distress syndrome, and sepsis or shock, were the single greatest risk factor for VTE in both groups. In the private insurance group, these complications were associated with an adjusted odds ratio (aOR) for VTE of 15.25 (95% CI, 13.86 - 16.79). In the Medicaid group, the aOR was 17.96 (95% CI, 16.03 - 20.12).

Postpartum infection was another important risk factor, associated with odds ratios of 6.76 (95% CI, 5.68 - 8.04) and 4.75 (95% CI, 3.86 - 5.84), respectively. Anemia, preeclampsia or eclampsia, smoking, obesity, and age also were prominent risk factors.

Pregnancy-related risk factors may be "mediated through their effects on coagulability and inflammation," the authors write. "In addition, acute perturbations such as hemorrhage or infection may compound the changes associated with the postpartum hemostatic system to further increase venous thromboembolism formation.... By 12 weeks, much of this remaining increase in risk may be attributable to the obstetric complication or other risk factor rather than postpartum status."

The researchers did not validate VTE diagnoses with medical records, so some of the cases may have been misclassified. Other possible study limitations include variations in the overall validity of diagnostic codes in administrative databases, leading to errors in estimating the association between certain risk factors and VTE; the inability to examine for certain risk factors associated with VTE, such as prior VTE or thrombophilia; and restricting the analysis to only the first delivery.

Nevertheless, the authors conclude, "The risk of postpartum venous thromboembolism is highest in the immediate postpartum period, and older women and women with obstetric complications are at higher risk. In addition, obstetric factors and complications confer an elevated risk during both the early and later postpartum period." The findings emphasize "the need for clinicians to have heightened awareness of the elevated and prolonged risk of postpartum venous thromboembolism, particularly among women with obstetric complications."

The authors have disclosed no relevant financial relationships.

Obstet Gynecol. 2014;123:987-996.


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