Recommendations for the prevention of pregnancy‐associated venous thromboembolism

Abstract

Pregnancy is a risk factor for venous thromboembolism (VTE), an important cause of maternal morbidity and mortality. Although there is a 4-5-fold increased risk compared to that of nonpregnant women of the same age, the absolute risk is low at no more than two episodes of VTE per 1000 pregnancies. There is uncertainty about which women require thromboprophylaxis during pregnancy or postpartum because of a lack of data from appropriate clinical trials. For this reason, recommendations for prophylaxis should be made only after explaining the available evidence to the patient and taking into account her perception of the balance of risk and benefit in thromboprophylaxis. The aim of these recommendations is to provide clinicians with practical advice to assist in decisions regarding thromboprophylaxis in women considered to be at risk of VTE during pregnancy and the postpartum. The authors are clinicians from across New Zealand and Australia representing the fields of haematology, obstetric medicine, anaesthesiology, maternal-fetal medicine and obstetrics. Authors were invited to review the relevant literature and then worked collaboratively to devise recommendations and resolve areas of controversy. The recommendations contained herein were reached by consensus and represent the opinion of the panel. The absence of randomised clinical trials in this area limits the strength of evidence that can be used, and it is acknowledged that they represent level C evidence. The panel advocates for appropriate clinical studies to be carried out in this patient population to address the inadequacy of present evidence.

Postpartum venous thromboembolism prophylaxis may cause more harm than benefit: a critical analysis of international guidelines through an evidence‐based lens

“…Obstetric VTE guidelines from the ACCP, Australia, Canada, New Zealand, Sweden and the Royal College of Obstetricians and Gynaecologists (RCOG) are based on case–control studies reporting relative risks of VTE in women with various risk factors and screening studies that report asymptomatic DVT 19, 20, 21, 22, 23. Risk‐scoring systems based on these data have not been validated.…”

Anticoagulation in pregnancy and puerperium: With a focus on the benefits and risks of the applications of vitamin K antagonists on the prevention of mechanical heart valves thrombosis

“…Pregnancy is a condition of increased risk of thrombosis due to synergy of all the three components of the Virchow's triad [2]. Due to altered physiology in pregnant women and hormonal status procoagulant factors and the procoagulant state dominates.…”

“…A series of homeostatic changes induced in pregnancy is associated with activated protein C resistance registered in a number of pregnant women [3][4][5]. Also, there is an increase in platelet-endothelial adhesion molecules as well as endothelial cell activation associated with a proinfl ammatory state, especially during labour or caesarean section when damage to blood vessels is incurred [2,6,7].…”

“…Consequently, in certain conditions during pregnancy there is a need for administering adequate anticoagulant therapy. Some diseases and conditions require the use of vitamin K antagonists (VKA), whose teratogenic potential presents a signifi cant safety issue [2]. Th ough VKA administration represents the most eff ective anticoagulant therapy for the prevention of thrombosis in pregnant women with mechanical heart valves, at the same time it may lead to serious birth defects, embryopathy, even stillbirth [8].…”

“…Th e risk of thrombosis in practice may be reduced by using higher doses of LMWH, more frequent testing and adjusting not only peak anti-Xa activity levels analyzed from a blood sample 4 h aft er subcutaneous injection of LMWH, but also trough anti-Xa activity levels, analyzed in the blood sample immediately prior to the administration of subcutaneous injections of LMWH. When administering LMWH in order to prevent thrombosis prosthetic valves, it is advised to maintain anti Xa activity values at a high therapeutic level [2].…”