Although our findings demonstrate increasing use of postcesarean mechanical prophylaxis, at the end of the study period, there was still significant underuse of this recommended means of reducing maternal morbidity and mortality. Although research in obstetric populations is limited, medical and surgical evidence supports mechanical prophylaxis as an effective means to reduce thromboembolism.42,43 Compression stockings and intermittent pneumatic compression devices are rarely contraindicated in obstetric patients and universal postcesarean mechanical prophylaxis is recommended by the American College of Obstetricians and Gynecologists.9
Our findings support the need for clear guidelines and protocols for thromboembolism prophylaxis. Not only did fewer than half of patients receive thromboembolism prophylaxis in 2010, but significant variation based on hospital factors occurred as well, suggesting uneven care quality. Suboptimal prophylaxis rates may be attributable in part to lack of clear indications for prophylaxis. Medical and obstetric risk factors were generally associated with only marginally higher risks of thromboprophylaxis and because multiple variables were tested for some significant associations may be the result of chance. Outside of a personal history of thromboembolism that carries high risk for postpartum recurrence, indications for thromboprophylaxis are not well defined and many risk factors are relatively common. Given the relative complexity of epidemiologic risk factors, a clinical decision regarding prophylaxis may be cumbersome, time-consuming, and complicated for many health care providers. The causes of increased prophylaxis at intermediate-volume and rural hospitals is unclear; however, it possible that hospital size and location may be related to the ability to quickly adopt clinical protocols. Risk assessment tools that simplify decision-making may aid hospitals in providing uniform, high-quality care.
Data from this study showed pharmacologic prophylaxis was used in only a small percentage of patients, much less frequently than would be indicated by British and Scandinavian guidelines.11,12 Although mechanical prophylaxis alone has been demonstrated to reduce deep vein thrombosis, reliance solely on this method for postoperative venous thromboembolism prophylaxis has well-documented shortcomings. First, studies of postoperative patients have demonstrated suboptimal compliance44 and studies evaluating educational programs directed at hospital personnel intended to improve compliance have not shown benefit.45 Second, because there are many devices on the market, and because even with high-risk surgeries, venous thromboembolism events are relatively rare, adequately powered studies validating individual device performance are lacking.46–48 Third, because many risk factors for increased thromboembolism risk such as preeclampsia, cesarean delivery during labor, and obesity are relatively common, many patients may still have a significant residual risk for events even if they receive mechanical prophylaxis. Low use of pharmacologic prophylaxis may be secondary to the fact that although research has found that for high-risk procedures, combination thromboprophylaxis with heparin offers greater risk reduction than mechanical prophylaxis alone,49 randomized trials focusing on effectiveness of pharmacologic prophylaxis after cesarean delivery are underpowered to assess outcomes and are inconclusive.40 The relative benefits of pharmacologic prophylaxis may be greater than suggested by prior decision analysis work7 because of the lower incidence of heparin-induced thrombocytopenia associated with low-molecular-weight heparins.50
Although our study benefits from the inclusion of a large cohort of patients in diverse geographic and hospital settings, we recognize important limitations. First, the primary purpose of claims data is billing and we cannot exclude the possibility of prophylaxis misclassification in some patients. However, this number is likely small because the hospitalization database has been validated in several studies that examine drug and device use.49,51,52 Second, although it is possible to estimate the number of patients who received prophylaxis, we are not able to examine the quality of prophylaxis. As already noted, compliance with mechanical prophylaxis among patients is poor. Third, because administrative data do not allow for direct determination of patient attributes such as body mass index, it is likely that the prevalence of some clinical risk factors is underestimated. Additionally, reported use of pharmacologic prophylaxis does not ensure that the proper dose of the drug was administered throughout the hospitalization. Finally, like with any observational study, we are unable to capture individual patient and physician preferences that likely influence prophylaxis.
In conclusion, as of 2010, fewer than half of women who underwent cesarean delivery received venous thromboembolism prophylaxis with significant variation noted despite an increased adoption of prophylaxis overall since 2003. Although patients at high risk for venous thromboembolism were more likely to receive mechanical prophylaxis, pharmacologic prophylaxis was rarely used. Thromboembolism prophylaxis is underused and represents a major opportunity to reduce maternal morbidity and mortality. Risk assessment tools and thromboprophylaxis guidelines among other validated measures are needed to assure high-quality, uniform care. Comparative effectiveness research is needed to further characterize the safety, efficacy, and cost of different prophylactic devices, medications, and regimens.
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