Anti-Xa Monitoring of Low-Molecular-Weight Heparin during Pregnancy: A Systematic Review

Low-molecular-weight heparin (LMWH) is commonly used for preventing or treating venous thromboembolic disease (VTE) during pregnancy. The physiological changes in maternal metabolism have led to discussions on optimal LMWH dosing strategy and possible need for monitoring. The aim of this systematic review is to summarize and discuss whether LMWH dose adjustment according to anti-Xa provides superior effectiveness and safety compared with weight adjusted or fixed dosed LMWH in pregnant women. A systematic literature search was performed in PubMed, Embase, and Scopus on September 26, 2020. The study is reported according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Effectiveness was defined as episodes of thrombosis and safety as bleeding episodes. In total, 33 studies were included: 4 randomized controlled studies and 29 cohort studies. Prophylactic dosing strategies employing weight dosed, fixed dosed, or anti-Xa adjusted LMWH dosing performed equal in effectiveness and safety. In pregnant women with VTE or high thromboembolic risk, therapeutic weight-adjusted LMWH and weight plus anti-Xa-adjusted LMWH provided equal results in terms of effectiveness and safety. Pregnant women with mechanical heart valves (MHVs) received therapeutic anti-Xa-adjusted LMWH with four out of seven studies presenting mean peak anti-Xa within target ranges. Still, pregnant women with MHV experienced both thrombosis and bleeding with anti-Xa in target. Based on the results of this systematic review, current evidence does not support the need for anti-Xa monitoring when using LMWH as thromboprophylaxis or treatment during pregnancy. Nonetheless, the need for anti-Xa monitoring in pregnant women with MHV may need further scrutiny.

Do Anti-Factor Xa Levels have any Impact on Pregnancy Outcome in Women with Previous Adverse Outcomes?

OBJECTIVE

Low-molecular-weight heparin (LMWH) is used during pregnancy in women diagnosed with thrombophilia for prevention of thromboembolic events and prevention of recurrent pregnancy loss. Prophylactic dosing does not always achieve target anti-FXa levels of 0.2-0.6 IU/ml. We aimed to determine if anti-FXa levels, measured in the first trimester, have an influence on pregnancy outcome.

MATERIAL AND METHODS

Eighty-one first-trimester women with a history of adverse pregnancy outcomes under LMWH therapy during pregnancy were enrolled in this study. Anti-FXa levels were measured in the first trimester, and fetal and maternal outcomes were recorded.

RESULTS

The mean age of women was 28±4 (19-40) and mean anti-FXa level 0.44±0.93 IU/ml. No bleeding or clotting complications were associated with LMWH administration. Anti-FXa levels did not have a relationship with gestational age at birth, fetal weight, type of delivery, cesarean indications, postpartum bleeding, APGAR scores, or admission to the neonatal intensive care unit (p>0.005). Anti-FXa levels were not correlated with live birth rates.

CONCLUSION

Anti-FXa levels did not have an influence on pregnancy and fetal outcomes. The effect of LMWH on pregnancy outcomes may not be due to anticoagulant activity but other mechanisms.

Management of Venous Thromboembolism in Pregnancy

PURPOSE OF REVIEW

This manuscript addresses the risks for venous thromboembolism (VTE) during pregnancy and the associated challenges of both diagnosis and treatment.

RECENT FINDINGS

The obstacles to diagnosis given lack of specificity of typical biomarkers to predict VTE in pregnancy, as well as the unique fetal and bleeding risks introduced by managing massive pulmonary embolism (PE) with thrombolytics or thrombectomy are highlighted. VTE during pregnancy and the postpartum window occurs at a 6-10-fold higher rate compared with age-matched peers and is a major cause of morbidity and mortality. Hypercoagulability persists for 6-8 weeks after delivery with the highest risk of PE being postpartum. The lack of randomized trials in pregnant women leads to variability in practice, which are largely based on expert consensus or extrapolation from non-pregnant cohorts. The standard treatment of VTE in pregnancy is anticoagulation with low molecular weight heparin (LMWH), which like unfractionated heparin does not cross the placenta and is not teratogenic. LMWH is preferred given the negligible risk for heparin-induced thrombocytopenia and osteoporosis, better bioavailability, and a predictive dose response. Depending on the severity of the VTE, additional treatments including thrombolysis, thrombectomy, inferior vena cava filter placement, or venous stenting may be used. Management requires balancing the competing bleeding and thrombotic risks during labor and delivery and factoring the impact of treatment on the fetus. A multidisciplinary team involving hematology, obstetrics, anesthesia, vascular medicine, and cardiology is critical for safe and timely management. The design and execution of prospective, randomized trials to specifically address optimal diagnosis and management are a top priority in obstetric hematology.