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Heparin-based thromboprophylaxis in obstetric patients did not reduce risk of venous thromboembolism (VTE), but may have increased the risks of other postpartum complications, a single-center retrospective study found.

While patients were nearly 15 times more likely to receive heparin-based thromboprophylaxis after the facility adopted a standardized protocol, there was no difference in VTE frequency between pre-protocol and post-protocol groups (0.1% for both), reported Michelle Lu, MD, of the University of Alabama at Birmingham, and colleagues in .

However, the risk of postpartum wound hematomas doubled in the post-protocol group (adjusted OR 2.34, 95% CI 1.54-3.57), largely driven by an increase in superficial hematomas. There was no difference in deep wound hematomas between the two groups.

Additionally, unplanned surgical procedures increased significantly post-protocol (adjusted OR 1.29, 95% CI 1.06-1.57), and more patients required red blood cell transfusions (adjusted OR 1.34, 95% CI 1.16-1.55).

VTE is one of the leading causes of maternal mortality, making up about 9% of pregnancy-related deaths in the U.S., Lu's group noted. The risk of thromboembolism increases during pregnancy, and is even higher postpartum -- especially during the first week after delivery.

Medical societies including the and the currently recommend a risk-stratified approach to VTE prevention during pregnancy. While heparin-based thromboprophylaxis for VTE has been widely adopted, Lu and colleagues said that their study's results should call widespread use into question.

"Despite international recommendations for routine use of heparin-based thromboprophylaxis, evidence is lacking to substantiate its expanded use in general obstetric populations," they wrote. Until more specific risk-stratification criteria are developed, they suggested that current recommendations in the general obstetric population should be reconsidered.

In an , Andrew Kotaska, MD, of the Stanton Territorial Hospital in Yellowknife, Canada, said that this study provided "much-needed guidance" on the use of low-molecular-weight heparin for VTE.

He noted that there is little evidence -- and no randomized trials -- showing the benefit or harm of heparin for VTE in pregnant patients without significant risk factors, such as a history of VTE or potent thrombophilia. Yet in patients with common risk factors, including obesity, maternal age over 40, or cesarean delivery, some international organizations still recommend use.

"In the era of evidence-based medicine, it is remarkable that low-molecular-weight heparin prophylaxis has been widely disseminated without measurement of net benefit or harm," Kotaska wrote. "Without further evidence, no one in good conscience can say to a birthing woman with common risk factors that she will benefit from low-molecular-weight heparin."

Lu's group conducted this retrospective cohort study of all patients who delivered at their single tertiary care center from 2013 to 2018. Deliveries before 2016 were categorized as pre-protocol, while deliveries from 2016 to 2018 were categorized as post-protocol.

After the protocol went into effect, patients with specific risk factors, including those with prepregnancy obesity, older maternal age, history of VTE, and others, received low-molecular-weight heparin 40 mg subcutaneously once a day. Patients with a BMI of 40 or higher received a 40-mg dose twice daily.

Patients who received antepartum outpatient anticoagulation for VTE and those at high risk for VTE were excluded from the analysis. Types of VTEs (e.g., deep vein thrombosis, pulmonary embolism) were similar between groups.

There were no significant differences between the two groups in postpartum readmissions, intensive care unit admissions, or maternal deaths.

Lu and colleagues recognized that there was heightened awareness of VTE frequency and wound hematomas after the protocol was introduced at their center, which may have introduced bias into the study's results. Additionally, their analysis included a small number of patients who may have received inpatient prophylactic anticoagulation during pregnancy.

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