New Guidance on Preventing Thromboembolism During Pregnancy

Nicola M. Parry, DVM

September 12, 2016

Current research data and guidelines on reducing maternal thromboembolism risk have been incorporated into a consensus safety bundle from the National Partnership for Maternal Safety, published online September 5 in Obstetrics & Gynecology. However, some specialists express concern that the consensus statement relies too heavily on pharmacologic prophylaxis without sufficient evidence to justify the approach.

According to Mary E. D'Alton, MD, from the Columbia University College of Physicians and Surgeons, New York City, and colleagues, "the thromboembolism bundle is not a new guideline but rather represents a selection of existing guidelines and recommendations in a form that aids implementation and consistency of practice that is appropriate for the individual birthing facility."

Venous thromboembolism (VTE) during pregnancy is a leading cause of maternal morbidity and mortality, with pulmonary thromboembolism accounting for an estimated 9.3% of pregnancy-related deaths in the United States.

Although maternal death from VTE is preventable by implementing comprehensive thromboembolism prevention strategies, prophylaxis guideline recommendations from medical and surgical specialties can differ substantially. In addition, clinical trial data remain lacking for the guidance of thromboprophylaxis in pregnancy.

In the United Kingdom, guidelines from the Royal College of Obstetricians and Gynaecologists (RCOG) recommend broad, risk-based assessments for antepartum and postpartum women to guide thromboprophylaxis. As a result, many women receive pharmacologic thromboprophylaxis, including, for example, most women who undergo cesarean delivery. Indeed, data have shown a significant reduction in maternal deaths from VTE in the United Kingdom since release of the RCOG guidelines.

Currently, in the United States, however, only women at highest risk for VTE receive pharmacologic thromboprophylaxis. Data have also shown an increased rate of obstetric VTE in the United States in recent decades, with no change in its associated rate of maternal deaths.

On the basis of these findings, the National Partnership for Maternal Safety therefore critically reviewed current guidelines and research evidence and made recommendations for prophylaxis. The safety bundle contains recommendations within four major areas.

Readiness, Recognition, Response, Reporting and Systems Learning

Readiness: The authors recommend that all pregnant women undergo risk assessment for VTE throughout pregnancy. In particular, clinicians should assess patients during the first prenatal visit, during any antepartum hospitalizations, immediately postpartum during a hospitalization for childbirth, and after they are discharged home after a delivery. Clinicians should use standardized risk-assessment tools such as the Caprini and Padua scoring systems.

Recognition: On the basis of results of this risk assessment, clinicians should use a patient's modified Caprini or Padua score to identify those who are at high risk for VTE, and who are therefore candidates for thromboprophylaxis.

Response: Women at high risk for VTE should receive appropriate thromboprophylaxis, according to their clinical situation and risk factors. Thromboprophylaxis strategies are based on guidelines from the American College of Obstetricians and Gynecologists, the American College of Chest Physicians, and the RCOG.

For example, for antepartum outpatient prophylaxis, the authors recommend treatment-dose low-molecular-weight (LMW) heparin or unfractionated heparin (UFH) for women with a clinical history of multiple VTE episodes, VTE with high-risk thrombophilia, or VTE with acquired thrombophilia.

For all antepartum patients who are hospitalized for 3 days or longer who are not at high risk for bleeding or imminent childbirth, they recommend prophylaxis with daily LMW heparin or twice-daily UFH.

For women with a history of VTE or thrombophilia who are undergoing a vaginal delivery, the authors recommend intrapartum mechanical thromboprophylaxis using pneumatic compression devices while in bed. Postpartum prophylaxis with LMW heparin or UFH may also be used for those at high risk for VTE based on RCOG criteria or a Padua score of 4 or greater.

Women undergoing cesarean delivery who are not receiving pharmacologic thromboprophylaxis should also receive perioperative mechanical thromboprophylaxis. Depending on their specific risk factors, these women should also receive postoperative pharmacologic thromboprophylaxis with LMW heparin or UFH, based on RCOG criteria or modified Caprini scores. However, because of the difficulty in identifying women at high risk for VTE, as well as problems related to poor compliance with mechanical devices, hospitals may choose to administer postoperative thromboprophylaxis with LMW heparin or UFH to all women undergoing cesarean delivery, unless there is a specific contraindication. This is consistent with RCOG recommendations, the authors note.

The authors also recommend extended postpartum pharmacologic thromboprophylaxis after hospitalization for childbirth. For example, women with a clinical history of multiple VTE episodes, VTE with high-risk thrombophilia, or VTE with acquired thrombophilia should receive a 6-week treatment-dose of LMW heparin or UFH.

Reporting and Systems Learning: All centers should review their patients' medical records to determine the prevalence of risk factors for VTE to develop thromboprophylaxis protocols. They should then routinely audit medical records to ensure clinicians are following risk assessment and thromboprophylaxis policies. Centers should also monitor patients for adverse events and complications from pharmacologic thromboprophylaxis.

The authors emphasize that all centers providing obstetric care should implement these critical clinical practices. "Although we recognize the need to individualize the specific details of these protocols to fit available resources, every unit should strive to implement prophylaxis strategies incorporating leadership from anesthesiology, obstetrics, midwifery, and nursing," they conclude.

However, in an accompanying editorial, Baha M. Sibai, MD, from the University of Texas Medical School at Houston, and Dwight J. Rouse, MD, MSPH, associate editor for Obstetrics & Gynecology, emphasize concern that "the marked expansion of pharmacologic prophylaxis that would occur with implementation of their recommendations is not justified by the available data and has the very real potential of doing more harm than good".

In particular, they note that recommendations to use the modified Padua and Caprini scoring systems, and to use antepartum prophylaxis with UFH for women hospitalized for 3 days or longer, are based on relatively low-quality evidence from studies involving nonobstetric populations.

The recommendation to use pharmacologic prophylaxis after vaginal delivery in women at high risk for VTE is also unclear, they add. "Because most women will be discharged 48 hours after vaginal delivery, do they recommend 2 days or 6 weeks of prophylaxis?"

Postcesarean Mechanical Thromboprophylaxis Is a Must

However, the editorialists' greatest concern is about the recommendation to use pharmacologic prophylaxis after cesarean delivery in women with risk factors, based on the RCOG criteria. This would apply to more than half of all cesarean deliveries in the United States, they say. Similarly, they question the rationale that hospitals may choose to administer pharmacologic prophylaxis to all women undergoing cesarean delivery, because of challenges related to identifying women at high risk for VTE, and in compliance with mechanical devices. They stress that, "[e]ven if adding pharmacologic prophylaxis to mechanical prophylaxis further reduced the rate of fatal pulmonary embolism by half (an effectiveness yet to be demonstrated), approximately 1 million women would require pharmacologic prophylaxis to prevent even one maternal death from cesarean delivery–associated pulmonary embolism."

Dr Sibai and Dr Rouse summarize that adoption of these recommendations would lead to exposure of millions of pregnant women to pharmacologic thromboprophylaxis that is of unproven benefit, yet is associated with recognized harms and is costly.

Nevertheless, recognizing the need to improve the management of obstetric VTE, Dr Sibai and Dr Rouse recommend a two-tiered approach: On a clinical level, all obstetric units should maximize compliance with postcesarean mechanical thromboprophylaxis, they say, and on an academic level, they stress the need for prospective data from large, well-characterized cohorts of obstetric patients in whom mechanical thromboprophylaxis has been implemented and used extensively.

This approach represents a reasonable middle ground that would provide baseline data about the rate of VTE against which to assess the benefits, harms, and cost-effectiveness of using pharmacologic thromboprophylaxis in obstetric patients, they conclude.

The authors and editorialists have disclosed no potential conflicts of interest.

Obstet Gynecol. Published online September 8, 2016. Article abstract, Editorial extract

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