Thrombogenesis in Thrombophilic Pregnancy: Evaluation of Low-Molecular-Weight Heparin Prophylaxis

How can Secondary Thromboprophylaxis in High-Risk Pregnant Patients be Improved?

Low-molecular-weight heparin (LMWH) is suggested for thromboprophylaxis in pregnant women with previous venous thromboembolism (VTE). Anyway, there is only limited amount of studies evaluating the effect of LMWH on hemostatic parameters during pregnancy of patients with previous VTE and the need of secondary thromboprophylaxis. We therefore provide results of prospective and longitudinal assessment of changes in hemostasis in high-risk pregnant women at four times during pregnancy (T1–T4) and one time after the postpartum period (T5) used for individualized modification of thromboprophylaxis. In this study, the results of coagulation factor VIII (FVIII) and protein S (PS) activity, ProC Global ratio and anti-Xa activity were evaluated. Despite the thromboprophylaxis, an increased predisposition to thromboembolic complications was detected (significant increase in FVIII activity and decrease in PS function, ProC Global ratio not normalized even after the postpartum period – p < .0001 between controls and T5 for PS and ProC Global). These results indicate that hemostasis may not be restored even 6 to 8 weeks after delivery and pose the question when is it safe to withdraw the anticoagulant thromboprophylaxis in high-risk patients with prior VTE.

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.

Obstetric venous thromboembolism: a systematic review of dalteparin and pregnancy

A systematic review of studies published between 1 January 1985 and 31 August 2017 was performed to analyse the efficacy of the low-molecular-weight heparin, dalteparin, in venous thromboembolism (VTE) treatment and prophylaxis during pregnancy, and to evaluate dosing practices, anticoagulant monitoring and adverse events. A therapeutic dosing throughout pregnancy or followed by reduced doses effectively prevented VTE recurrence. Anti-factor Xa activity was the most commonly used method of dose monitoring. The risk of bleeding with dalteparin was generally minor. Major bleeding was observed when a high dose of dalteparin was employed during (or close to) delivery, or postpartum. Other adverse events were minor. Disparity exists in VTE treatment and thromboprophylaxis, with wide variety in the dosing regimens, treatment strategies and monitoring practices employed. Large randomised controlled trials are warranted but due to ethical reasons, and the rarity of VTE-associated obstetric complications, case-control, registry and large observational studies present more likely options.