Low molecular weight heparin to prevent postpartum venous thromboembolism: A pilot study to assess the feasibility of a randomized, open-label trial

Preferences of pregnant women for postpartum thromboprophylaxis: the bicentric PREFER-PostPartum study

BACKGROUND

Clinical guidelines for postpartum thromboprophylaxis differ due to its uncertain effect and varying preferences of experts. Women's preferences for postpartum thromboprophylaxis are unknown, although they may inform practices and future research.

OBJECTIVES

Our aim was to elicit the pregnant women's preferences for postpartum thromboprophylaxis according to different risks of venous thromboembolism (VTE) and bleeding.

METHODS

In 2 Swiss and French maternity hospitals, we conducted structured interviews of pregnant or postpartum women. Participants were instructed on pulmonary embolism, deep vein thrombosis, postpartum hemorrhage, and subcutaneous injections of low-molecular-weight heparin (LMWH). First, we randomized women to either standard gamble or time trade-off (2 different validated methods) to estimate the utilities (quality of life, from 0 to 1) of these health states. Second, we elicited the preference for the use of short-term postpartum thromboprophylaxis with LMWH vs none across different risks of postpartum VTE and bleeding through direct-choice exercises.

RESULTS

Among 122 participants, median (IQR) health state utilities were 0.725 (0.30-0.925) for pulmonary embolism, 0.75 (0.40-0.97) for postpartum hemorrhage, 0.85 (0.60-0.97) for deep vein thrombosis, and 0.96 (0.96-0.999) for LMWH injections. The median risk of postpartum VTE for preference of the use of postpartum thromboprophylaxis over no treatment was 0.1% (IQR, 0.01%-0.50%) without LMWH-associated bleeding risk and 0.2% (IQR, 0.1%-5%) with a 1% bleeding risk.

CONCLUSION

European pregnant women appear to have a high willingness for 10-day postpartum thromboprophylaxis, preferred over no treatment even for low risks of postpartum VTE. This perspective from patients supports the urgent need for a randomized trial evaluating the efficacy and safety of postpartum thromboprophylaxis.

Preventing Postpartum Venous Thromboembolism With Low-Molecular-Weight Heparin: The PP-HEP Pilot Randomised Controlled Trial

OBJECTIVE

Uncertainty surrounds the risk-benefit of low-molecular-weight heparin to prevent postpartum venous thromboembolism (VTE). Data from randomised clinical trials (RCT) are critically needed, but recent feasibility studies in North America yielded low participation rates, with <1 enrolment per month per centre. Our aim was to assess the feasibility of a trial of postpartum short-term enoxaparin in Europe.

DESIGN

Pragmatic, open-label pilot randomised controlled trial (RCT).

SETTING

Swiss tertiary hospital.

POPULATION

Postpartum women, within 48 h of delivery, deemed at intermediate risk of VTE with at least one major risk factor (morbid obesity, thrombophilia, emergency caesarean section, pre-eclampsia, preterm delivery, intrauterine growth restriction or systemic peripartum infection) and/or at least two minor risk factors.

METHODS

Participants were randomised to enoxaparin 40-60 mg once daily for 10 days or no treatment, with a 90-day follow-up.

MAIN OUTCOME MEASURES

Participation rate and study acceptance (randomised participants among women in whom informed consent was sought).

RESULTS

Recruitment was open for 25 weeks in 2022. Among 1504 postpartum women, 480 were eligible and 77 were randomised. The recruitment rate was 3.1 per week (13.3 per month) and the study acceptance was 23.8%. At 3 months, there was no VTE event, but one major, one nonmajor obstetrical bleeding and one surgical site complication, all in the enoxaparin group.

CONCLUSIONS

This pilot RCT of postpartum thromboprophylaxis set in Switzerland yielded greater participation rate and acceptance than previous attempts in North America. It calls for a large, international, collaborative trial to guide this important clinical decision.

TRIAL REGISTRATION

ClinicalTrial.gov identifier: NCT05878899 and NCT04153760.

VTE Risk Assessment and Prevention in Pregnancy

Venous thromboembolism (VTE) remains the leading cause of maternal mortality in pregnancy and the postpartum period. In addition to the higher pregnancy-associated baseline VTE risk, there are several well-established risk factors that can further increase the risk of VTE. At present, a thorough interrogation of these risk factors remains our only tool for estimating which pregnant people may be at an increased risk of VTE, and thus potentially benefit from thromboprophylaxis. However, an important knowledge gap still exists surrounding the duration of increased risk and the interaction of risk factors with each other. Furthermore, up to now, once significant risk has been established, prevention strategies have been largely based on expert opinion rather than high-quality data. Recent trials have successfully bridged a proportion of this knowledge gap; however, the challenge of conducting high-quality clinical trials with pregnant people remains. In this article, we provide an update on the recent evidence surrounding VTE risk factors in pregnancy while concurrently outlining knowledge gaps and current approaches to VTE prevention.

Estimating the value of future research into thromboprophylaxis for women during pregnancy and after delivery: a value of information analysis

BACKGROUND

Risk assessment models (RAMs) are used to select women at increased risk of venous thromboembolism (VTE) during pregnancy and the puerperium for thromboprophylaxis.

OBJECTIVES

To estimate the value of potential future studies that would reduce the decision uncertainty associated with offering thromboprophylaxis according to available RAMs in the following groups: high-risk antepartum women (eg, prior VTE), unselected postpartum women, and postpartum women with risk factors (obesity or cesarean delivery).

METHODS

A decision-analytic model was developed to simulate clinical outcomes, lifetime costs, and quality-adjusted life-years for different thromboprophylaxis strategies, including thromboprophylaxis for all, thromboprophylaxis for none, and RAM-based thromboprophylaxis. The expected value of perfect information analysis was used to determine which factors are associated with high decision uncertainty. The value of future research studies was estimated using expected value of sample information analysis. Costs were assessed from a health and social services perspective.

RESULTS

The expected value of perfect information analysis identified high decision uncertainty for high-risk antepartum women (£21.8 million) and obese postpartum women (£13.4 million), which was largely attributable to uncertainty regarding the effectiveness of thromboprophylaxis in reducing VTE. A randomized controlled trial of thromboprophylaxis compared with none in obese postpartum women is likely to have substantial value (£2.8 million; 300 participants per arm). A trial in women with previous VTE would have higher value but would be less acceptable.

CONCLUSION

Future research should focus on estimating the effectiveness of thromboprophylaxis in obese postpartum women with additional risk factors who have not had a previous VTE.

Thromboprophylaxis during pregnancy and the puerperium: a systematic review and economic evaluation to estimate the value of future research

Background

Pharmacological prophylaxis to prevent venous thromboembolism is currently recommended for women assessed as being at high risk of venous thromboembolism during pregnancy or in the 6 weeks after delivery (the puerperium). The decision to provide thromboprophylaxis involves weighing the benefits, harms and costs, which vary according to the individual's venous thromboembolism risk. It is unclear whether the United Kingdom's current risk stratification approach could be improved by further research.

Objectives

To quantify the current decision uncertainty associated with selecting women who are pregnant or in the puerperium for thromboprophylaxis and to estimate the value of one or more potential future studies that would reduce that uncertainty, while being feasible and acceptable to patients and clinicians.

Methods

A decision-analytic model was developed which was informed by a systematic review of risk assessment models to predict venous thromboembolism in women who are pregnant or in the puerperium. Expected value of perfect information analysis was used to determine which factors are associated with high decision uncertainty and should be the target of future research. To find out whether future studies would be acceptable and feasible, we held workshops with women who have experienced a blood clot or have been offered blood-thinning drugs and surveyed healthcare professionals. Expected value of sample information analysis was used to estimate the value of potential future research studies.

Results

The systematic review included 17 studies, comprising 19 unique externally validated risk assessment models and 1 internally validated model. Estimates of sensitivity and specificity were highly variable ranging from 0% to 100% and 5% to 100%, respectively. Most studies had unclear or high risk of bias and applicability concerns. The decision analysis found that there is substantial decision uncertainty regarding the use of risk assessment models to select high-risk women for antepartum prophylaxis and obese postpartum women for postpartum prophylaxis. The main source of decision uncertainty was uncertainty around the effectiveness of thromboprophylaxis for preventing venous thromboembolism in women who are pregnant or in the puerperium. We found that a randomised controlled trial of thromboprophylaxis in obese postpartum women is likely to have substantial value and is more likely to be acceptable and feasible than a trial recruiting women who have had a previous venous thromboembolism. In unselected postpartum women and women following caesarean section, the poor performance of risk assessment models meant that offering prophylaxis based on these models had less favourable cost effectiveness with lower decision uncertainty.

Limitations

The performance of the risk assessment model for obese postpartum women has not been externally validated.

Conclusions

Future research should focus on estimating the efficacy of pharmacological thromboprophylaxis in pregnancy and the puerperium, and clinical trials would be more acceptable in women who have not had a previous venous thromboembolism.

Study registration

This study is registered as PROSPERO CRD42020221094.

Funding

This award was funded by the National Institute for Health and Care Research (NIHR) Health Technology Assessment programme (NIHR award ref: NIHR131021) and is published in full in Health Technology Assessment; Vol. 28, No. 9. See the NIHR Funding and Awards website for further award information.

VTE risk assessment, prevention and diagnosis in pregnancy

Venous thromboembolism (VTE) is still reported as the leading cause of direct maternal death in pregnancy in serial international reports in developed countries. VTE risk is higher during pregnancy but is further increased by additional well-characterized risk factors. International guidelines recommend that formal VTE risk assessment should be conducted at least in early pregnancy, at delivery and when risk factors change. High quality data supporting optimal VTE prevention strategies are lacking, outside the setting of prevention of VTE recurrence. Moreover, recent high-quality studies have provided much-needed data on diagnostic strategies for pulmonary embolism (PE) in pregnancy. In this review, we summarize knowledge gaps and recently published data in the prevention and diagnosis of VTE in pregnancy. Moreover, we describe ongoing high-quality randomised trials and prospective clinical management studies in this area. High quality clinical studies and trials in pregnancy can be done and must be prioritised, through international network efforts and national funding advocacy. Ultimately, translation of study results to impact upon guidelines and policy will deliver better care to and will protect the lives and health of pregnant people and those contemplating pregnancy throughout the world.

Projected impact of guidelines on incidence of venous thromboembolism after cesarean delivery in the United States

BACKGROUND

There is large variation in recommended for postcesarean delivery venous thromboembolism (VTE) prophylaxis among commonly used guidelines.

OBJECTIVES

The aim of the study is to estimate implications of adoption of VTE prevention guidelines for rates of receipt of VTE prophylactic therapy and VTE following cesarean delivery (CD).

METHODS

We used administrative data from the 2015-2019 Nationalwide Readmissions Database to identify cesarean deliveries and rates of VTE stratified by risk factors, leading to different prophylactic strategies based on several national guidelines. We used input parameters from the literature to construct a hybrid decision tree/Markov model to project the implications of guideline adoption on VTE rates for the first 6 weeks following delivery.

RESULTS

Adoption of either the 2011 American College of Obstetricians and Gynecologists or the 2018 American Society for Hematology guidelines would avert a relatively small proportion (5%) of VTE cases, albeit with little low-molecular-weight heparin (LMWH) use (87-115 doses per 1000 CD patients). The 2012 American College of Chest Physicians guidelines were predicted to be more effective at averting VTE (21.2% reduction) with more LMWH usage (570 doses per 1000 deliveries). The 2015 Royal College of Obstetricians and Gynaecologists guidelines and universal use of 6 weeks of LMWH would avert an even larger proportion of cases (37.4% and 57.6%, respectively), at the cost of much higher rates of LMWH utilization (7233 doses per 1000 patients and 38 648 doses per 1000 patients).

CONCLUSIONS

Adoption of different guidelines would have notably varying implications for clinical practice and potential for alteration of the national rate of VTE following CD.

Efficacy of Postpartum Pharmacologic Thromboprophylaxis: A Systematic Review and Meta-analysis

OBJECTIVE

To evaluate the effectiveness of pharmacologic venous thromboembolism (VTE) prophylaxis in postpartum patients.

DATA SOURCES

On February 21, 2022, a literature search was conducted on Embase.com, Ovid-Medline All, Cochrane Library, Scopus, and ClinicalTrials.gov using terms postpartum period AND thromboprophylaxis AND antithrombin medications including heparin and low molecular weight heparin.

METHODS OF STUDY SELECTION

Studies that evaluated the outcome of VTE among postpartum patients exposed to pharmacologic VTE prophylaxis with or without a comparator group were eligible for inclusion. Studies of patients who received antepartum VTE prophylaxis, studies in which this prophylaxis could not be definitively ruled out, and studies of patients who received therapeutic dosing of anticoagulation for specific medical problems or treatment of VTE were excluded. Titles and abstracts were independently screened by two authors. Relevant full-text articles were retrieved and independently reviewed for inclusion or exclusion by two authors.

TABULATION, INTEGRATION, AND RESULTS

A total of 944 studies were screened by title and abstract, and 54 full-text studies were retrieved for further evaluation after 890 studies were excluded. Fourteen studies including 11,944 patients were analyzed: eight randomized controlled trials (8,001 patients) and six observational studies (3,943 patients). Among the eight studies with a comparator group, there was no difference in the risk of VTE between patients who were exposed to postpartum pharmacologic VTE prophylaxis and those who were unexposed (pooled relative risk 1.02, 95% CI 0.29-3.51); however, six of eight studies had no events in either the exposed or unexposed group. Among the six studies without a comparator group, the pooled proportion of postpartum VTE events was 0.00, likely due to five of six studies having no events.

CONCLUSION

The current literature provided an insufficient sample size to conclude whether postpartum VTE rates differ between those exposed to postpartum pharmacologic prophylaxis and those unexposed, given the rarity of VTE events.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO, CRD42022323841.

Preventing Postpartum Venous Thromboembolism in 2022: A Narrative Review

The postpartum period represents the most critical time for pregnancy-associated venous thromboembolism (VTE), which is responsible for substantial morbidity and an important cause of maternal mortality. The estimated risk of postpartum VTE of about 1/1,000 deliveries can be modulated with the knowledge of maternal and obstetrical risk factors, although a precise estimate remains challenging in individuals. The use of postpartum low-dose low-molecular-weight heparins are tailored at intermediate and high-risk groups to reduce the thrombotic burden, despite the lack of dedicated randomized controlled trials. In this review, we will highlight the contemporary evidence on the risk of postpartum VTE, its stratification and its prevention. We will also discuss our knowledge on the values and preferences of women for postpartum thromboprophylaxis and their adherence to treatment.

Preeclampsia and Venous Thromboembolism: Pathophysiology and Potential Therapy

Preeclampsia (PET) is a multisystem inflammatory disorder that represents a leading cause of feto-maternal morbidity and mortality, complicating 2-5% of all pregnancies. PET incurs an increased risk of venous thromboembolism, which is one of the leading causes of death in pregnancy and in the postpartum period. This prothrombotic phenotype is attributable to the maternal phase of PET, which is characterized by a systemic inflammatory response and coagulation activation. Research continues to be undertaken in terms of preventative measures, however, currently revolves around pharmacological low dose aspirin initiated in the first trimester of pregnancy for those with risk factors. Treatment involves antenatal corticosteroids for fetal lung development in preterm birth, parenteral magnesium sulfate for fetal neuroprotection and maternal seizure prophylaxis, and timely birth of the fetus and placenta being the only definitive treatment of PET. Patients with a venous thromboembolism (VTE) risk deemed to be >1-3% are treated with pharmacological thromboprophylaxis in the form of low molecular weight heparin. Completing each woman's VTE risk assessment is crucial, particularly in the setting of PET, as there is also a proven associated competing hemorrhagic risk.

Prevention and management of venous thromboembolism in pregnancy: cutting through the practice variation

There is clinical practice variation in the area of prevention and management of venous thromboembolism (VTE) in pregnancy. There are limited data and differing recommendations across major clinical practice guidelines, especially relating to the role of postpartum low-molecular-weight heparin (LMWH) for patients with mild inherited thrombophilia and those with pregnancy-related VTE risk factors. This chapter explores the issues of practice variation and related data for postpartum VTE prevention. Controversial topics of VTE management in pregnancy are also reviewed and include LMWH dosing and the role of anti-Xa level monitoring, as well as peripartum anticoagulation management around labor and delivery.

Prophylaxis and management of venous thromboembolism during pregnancy and postpartum period

Introduction. Venous thromboembolism (VTE) is one of the lead causes for maternal mortality and morbidity during pregnancy in the majority of developed countries. The incidence rate of VTE per pregnancy-year increases during pregnancy and postpartum period about by 4-fold and at least 14-fold, respectively.

Aim: to analyze and summarize current view on risk factors of thrombotic events during gestation and to discuss recent guidelines for the management of venous thromboembolic complications during pregnancy and postpartum, by taking into account a balance between risks and benefits of using anticoagulants.

Materials and Methods. The literature search covering the last 10 years was carried out in the electronic scientific databases RSCI, PubMed/MEDLINE, and Embase. While formulating a search strategy for evidence-based information, the PICO method (P = Patient; I = Intervention; C = Comparison; O = Outcome) and the key terms “venous thromboembolism” and “pregnancy” were used.

Results. Risk factors were found to include a personal history of VTE, verified inherited or acquired thrombophilia, a family history of VTE and general medical conditions, such as immobilization, overweight, varicose veins, some hematological diseases and autoimmune disorders. VTE is considered being potentially preventable upon prophylactic administration of anticoagulants, but no high confidence randomized clinical trials comparing diverse strategies of thromboprophylaxis in pregnant women have been proposed so far. Because heparins do not cross the placenta, weight-adjusted therapeutic-dose low molecular weight heparins (LMWH) represent the anticoagulant treatment of choice for VTE during pregnancy. Once- and twice-daily dosing regimens are acceptable. However, no evidence suggesting benefits for measurement of factor Xa activities and consecutive LMWH dose adjustments to improve clinical outcomes are available. In case of uncomplicated pregnancy-related VTE, no routine administration of vitamin K antagonists, direct thrombin or factor Xa inhibitors, fondaparinux, or danaparoid is recommended. Lactating women may switch from applying LMWH to warfarin. Anticoagulation therapy should be continued for 6 weeks postpartum with total duration lasting at least for 3 months.

Conclusion. VTE is a challenging task in pregnant women expecting to apply a multi-faceted approach for its efficient solution by taking into account updated recommendations and personalized patient-oriented features.

Obstetric venous thromboembolism prophylaxis, risk factors and outcomes

PURPOSE OF REVIEW

Risk factors for obstetric venous thromboembolism (VTE), a leading cause of maternal mortality in the United States, are increasing on a population basis. This review provides the obstetrician with an update of current issues related to obstetric VTE risk, prophylaxis, outcomes, anaesthesia considerations and future research opportunities.

RECENT FINDINGS

Obstetric VTE affects approximately 1 per 1000 pregnancies and accounts consistently for 9-10% of maternal deaths in the United States. In industrialized countries, risk factors for VTE, including overweight/obesity, caesarean delivery and obstetrical complications such postpartum haemorrhage and infection continue to increase. VTE prophylaxis is central to reducing maternal mortality. However, recommendations for prophylaxis from leadership societies vary widely. In the UK, maternal mortality risk from VTE has decreased significantly in the setting of broader heparin prophylaxis. In the United States where mechanical VTE prophylaxis is used more commonly, mortality risk has remained constant.

SUMMARY

Obstetric VTE is a leading cause of maternal mortality in the United States. The incidence of risk factors for obstetric VTE continues to increase. Currently, recommendations for obstetric VTE prophylaxis vary substantially. Opportunities for research in this area exist to optimize prophylaxis and improve maternal outcomes.

Expert review: prevention of obstetrical venous thromboembolism

Venous thromboembolism represents a persistent proportionate cause of maternal mortality in the United States accounting for 9% to 10% of maternal deaths. Given that overall maternal mortality rose >40% since the late 1990s, it is likely that absolute venous thromboembolism mortality risk increased as well. This persistent risk may be secondary to increases in broad population-based risk factors for venous thromboembolism such as obesity and cesarean delivery. Widespread adoption of perioperative cesarean mechanical thromboprophylaxis is associated with reduced risk for venous thromboembolism events but has not been sufficient to reduce mortality. Experts agree that improved clinical care is required to reduce risk as it is unlikely that trends in venous thromboembolism risk factors will reverse course anytime soon. Experts further agree that improving prophylaxis and prevention may provide the largest benefit. However, how to best improve prophylaxis is highly controversial with both experts and guidelines in disagreement. In the United Kingdom, mortality risk decreased substantially following the 2004 recommendations for broader heparin prophylaxis without evidence of increased mortality risk from hemorrhage. A key clinical question in the United States is whether heparin prophylaxis should be expanded to patients hospitalized for cesarean delivery or an antepartum indication. Some experts, including us, support expanded heparin prophylaxis. Evidence supporting heparin prophylaxis includes (1) demonstration of safety and efficacy in the United Kingdom, (2) that mechanical prophylaxis-the primary alternative to heparin-has major limitations outside the immediate perioperative setting, and (3) that hospitalized cesarean and antepartum patients are at high relative risk of events. Experts against broader heparin prophylaxis cite concerns related to safety, efficacy, and cost. This expert review focused on whether heparin prophylaxis should be routinely used during antepartum hospitalizations and after cesarean delivery. First, we review the differences in major society guidelines. Second, we review arguments for and against broader heparin prophylaxis. Third, we discuss what future research may be most likely to further inform best practices. Fourth, we review practical clinical considerations with heparin prophylaxis, including access to neuraxial anesthesia. Given the best available data, we concluded that expanding heparin prophylaxis represents a modest intervention with the potential to meaningfully reduce venous thromboembolism mortality.

Prophylactic Anticoagulation With Intermediate-Dose Certoparin in Vascular-Risk Pregnancies-The PACER-VARP Registry

The management of pregnant women at increased risk of thromboembolic/other vascular events is still a matter of debate. In a single-center, retrospective, observational trial, we analyzed the safety and efficacy of prophylactic anticoagulation with certoparin in pregnant women at intermediate- or high-risk by EThIG criteria of thromboembolic/other vascular events. Subcutaneous certoparin 8,000 IU once daily was administered immediately after pregnancy confirmation and continued for 6 weeks postpartum. We investigated 74 pregnancies (49 women; mean age 31.8 years; weight 77.3 kg). Most prevalent risk factors were factor V Leiden mutation (40.5%), thrombogenic factor II mutation (12.2%) and protein S deficiency (8.1%). In 76 control pregnancies prior to registry inclusion/without anticoagulation there were 14 cases [18.4%] of venous thromboembolism (between week 7 gestation and week 8 postpartum); 63.2% pregnancies resulted in abortion (median week 8.6 gestation). With certoparin anticoagulation, thromboembolism was 1.4%, exclusively non-major bleeding was 4.1% and abortion was 10.8%. One case of pre-eclampsia necessitating obstetric intervention occurred. Prophylactic anticoagulation with intermediate-dose certoparin throughout pregnancies at increased venous vascular risk was safe and effective.

Venous thromboembolism prophylaxis for women at risk during pregnancy and the early postnatal period

BACKGROUND

Venous thromboembolism (VTE), although rare, is a major cause of maternal mortality and morbidity. Some women are at increased risk of VTE during pregnancy and the early postnatal period (e.g. caesarean section, family history of VTE, or thrombophilia), and so prophylaxis may be considered. As some methods of prophylaxis carry risks of adverse effects, and risk of VTE is often low, benefits of thromboprophylaxis may be outweighed by harms.

OBJECTIVES

To assess the effects of thromboprophylaxis during pregnancy and the early postnatal period on the risk of venous thromboembolic disease and adverse effects in women at increased risk of VTE.

SEARCH METHODS

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (18 October 2019). In addition, we searched ClinicalTrials.gov and the WHO International Clinical Trials Registry Platform (ICTRP) for unpublished, planned and ongoing trial reports (18 October 2019).

SELECTION CRITERIA

Randomised trials comparing one method of thromboprophylaxis with placebo or no treatment, or two (or more) methods of thromboprophylaxis.

DATA COLLECTION AND ANALYSIS

At least two review authors assessed trial eligibility, extracted data, assessed risk of bias, and judged certainty of evidence for selected critical outcomes (using GRADE). We conducted fixed-effect meta-analysis and reported data (all dichotomous) as summary risk ratios (RRs) with 95% confidence intervals (CIs).

MAIN RESULTS

Twenty-nine trials (involving 3839 women), overall at moderate to high risk of bias were included. Trials were conducted across the antenatal, peripartum and postnatal periods, with most in high-income countries. Interventions included types and regimens of heparin (low molecular weight heparin (LMWH) and unfractionated heparin (UFH)), hydroxyethyl starch (HES), and compression stockings or devices. Data were limited due to a small number of trials in comparisons and/or few or no events reported. All critical outcomes (assessed for comparisons of heparin versus no treatment/placebo, and LMWH versus UFH) were considered to have very low-certainty evidence, downgraded mainly for study limitations and imprecise effect estimates.  Maternal death was not reported in most studies. Antenatal (± postnatal) prophylaxis For the primary outcomes symptomatic thromboembolic events pulmonary embolism (PE) and/or deep vein thrombosis (DVT), and the critical outcome of adverse effects sufficient to stop treatment, the evidence was very uncertain.  Symptomatic thromboembolic events: - heparin versus no treatment/placebo (RR 0.39; 95% CI 0.08 to 1.98; 4 trials, 476 women; very low-certainty evidence); - LMWH versus UFH (RR 0.47; 95% CI 0.09 to 2.49; 4 trials, 404 women; very low-certainty evidence); Symptomatic PE: - heparin versus no treatment/placebo (RR 0.33; 95% CI 0.02 to 7.14; 3 trials, 187 women; very low-certainty evidence); - LMWH versus UFH (no events; 3 trials, 287 women); Symptomatic DVT: - heparin versus no treatment/placebo (RR 0.33; 95% CI 0.04 to 3.10; 4 trials, 227 women; very low-certainty evidence); - LMWH versus UFH (no events; 3 trials, 287 women); Adverse effects sufficient to stop treatment: - heparin versus no treatment/placebo (RR 0.49; 95% CI 0.05 to 5.31; 1 trial, 139 women; very low-certainty evidence); - LMWH versus UFH (RR 0.07; 95% CI 0.01 to 0.54; 2 trials, 226 women; very low-certainty evidence). Peripartum/postnatal prophylaxis Vaginal or caesarean birth When UFH and no treatment were compared, the effects on symptomatic thromboembolic events (RR 0.16; 95% CI 0.02 to 1.36; 1 trial, 210 women; very low-certainty evidence), symptomatic PE (RR 0.16; 95% CI 0.01 to 3.34; 1 trial, 210 women; very low-certainty evidence), and symptomatic DVT  (RR 0.27; 95% CI 0.03 to 2.55; 1 trial, 210 women; very low-certainty evidence) were very uncertain.  Maternal death and adverse effects sufficient to stop treatment were not reported. Caesarean birth Symptomatic thromboembolic events: - heparin versus no treatment/placebo (RR 1.30; 95% CI 0.39 to 4.27; 4 trials, 840 women; very low-certainty evidence); - LMWH versus UFH (RR 0.33; 95% CI 0.01 to 7.99; 3 trials, 217 women; very low-certainty evidence); Symptomatic PE: - heparin versus no treatment/placebo (RR 1.10; 95% CI 0.25 to 4.87; 4 trials, 840 women; very low-certainty evidence); - LMWH versus UFH (no events; 3 trials, 217 women);  Symptomatic DVT: - heparin versus no treatment/placebo (RR 1.30; 95% CI 0.24 to 6.94; 5 trials, 1140 women; very low-certainty evidence); LMWH versus UFH (RR 0.33; 95% CI 0.01 to 7.99; 3 trials, 217 women; very low-certainty evidence); Maternal death: - heparin versus placebo (no events, 1 trial, 300 women); Adverse effects sufficient to stop treatment: - heparin versus placebo (no events;  1 trial, 140 women). Postnatal prophylaxis No events were reported for LMWH versus no treatment/placebo for: symptomatic thromboembolic events, symptomatic PE and symptomatic DVT (all 2 trials, 58 women), or maternal death (1 trial, 24 women). Adverse effects sufficient to stop treatment were not reported. We were unable to conduct subgroup analyses due to lack of data. Sensitivity analysis including the nine studies at low risk of bias did not impact overall findings.

AUTHORS' CONCLUSIONS

The evidence is very uncertain about benefits and harms of VTE thromboprophylaxis in women during pregnancy and the early postnatal period at increased risk of VTE. Further high-quality very large-scale randomised trials are needed to determine effects of currently used treatments in women with different VTE risk factors. As sufficiently large definitive trials are unlikely to be funded, secondary data analyses based on high-quality registry data are important.

Preventing postpartum venous thromboembolism: A call to action to reduce undue maternal morbidity and mortality

Postpartum venous thromboembolism (VTE) is a leading cause of maternal mortality in developed countries and can carry significant long-term morbidity. Despite being able to identify postpartum VTE risk factors in a large proportion of the obstetrical population, there is little high-quality evidence available to guide practice on who should receive postpartum thromboprophylaxis. Based on epidemiological data, women with a prior history of VTE or known potent thrombophilia are likely to benefit from an extended duration of low-molecular-weight heparin (LMWH) prophylaxis. However, significant controversy exists around the benefit and harm of postpartum thromboprophylaxis in women with more modest risk factors, such as those with mild thrombophilias or transient situational risk factors around labor and delivery, such as cesarean delivery. We review the available data for postpartum VTE risk factors and thromboprophylaxis in these patients. This review highlights the latest evidence in the area of postpartum VTE prevention, and is a call to action for further research in this area to improve maternal morbidity and mortality.

VTE risk assessment in pregnancy

A State of the Art lecture, "VTE Risk Assessment in Pregnancy," was presented at the ISTH congress in Melbourne, Australia, in 2019. Venous thromboembolism (VTE) remains a leading cause of death in pregnancy and in the postpartum period. Moreover, VTE can result in lifelong disability. The elevated baseline pregnancy-associated VTE risk is further increased by additional maternal, pregnancy, and delivery characteristics, highlighting the importance of VTE risk assessment in early pregnancy, at delivery, and if risk factors change. This review will provide an overview of the impact and epidemiology of VTE in pregnancy (including reported risk factors for pregnancy-associated VTE), will address VTE risk-reduction strategies (including ongoing studies), and will provide a summary of critical knowledge gaps. Finally, throughout this review, relevant new data presented during the 2019 ISTH annual congress in Melbourne will be summarized.

American Society of Hematology 2018 guidelines for management of venous thromboembolism: venous thromboembolism in the context of pregnancy

BACKGROUND

Venous thromboembolism (VTE) complicates ∼1.2 of every 1000 deliveries. Despite these low absolute risks, pregnancy-associated VTE is a leading cause of maternal morbidity and mortality.

OBJECTIVE

These evidence-based guidelines of the American Society of Hematology (ASH) are intended to support patients, clinicians and others in decisions about the prevention and management of pregnancy-associated VTE.

METHODS

ASH formed a multidisciplinary guideline panel balanced to minimize potential bias from conflicts of interest. The McMaster University GRADE Centre supported the guideline development process, including updating or performing systematic evidence reviews. The panel prioritized clinical questions and outcomes according to their importance for clinicians and patients. The Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach was used to assess evidence and make recommendations.

RESULTS

The panel agreed on 31 recommendations related to the treatment of VTE and superficial vein thrombosis, diagnosis of VTE, and thrombosis prophylaxis.

CONCLUSIONS

There was a strong recommendation for low-molecular-weight heparin (LWMH) over unfractionated heparin for acute VTE. Most recommendations were conditional, including those for either twice-per-day or once-per-day LMWH dosing for the treatment of acute VTE and initial outpatient therapy over hospital admission with low-risk acute VTE, as well as against routine anti-factor Xa (FXa) monitoring to guide dosing with LMWH for VTE treatment. There was a strong recommendation (low certainty in evidence) for antepartum anticoagulant prophylaxis with a history of unprovoked or hormonally associated VTE and a conditional recommendation against antepartum anticoagulant prophylaxis with prior VTE associated with a resolved nonhormonal provoking risk factor.