Effectiveness and safety of thromboprophylaxis with enoxaparin for prevention of pregnancy-associated venous thromboembolism

Abstract

Essentials Thromboprophylaxis is offered to women considered to be at risk from pregnancy-associated venous thromboembolism (PA-VTE) but there is a suggestion that standard doses of low-molecular-weight heparin may not be effective. We conducted a large observational cohort study reviewing maternal outcomes in women who received extended thromboprophylaxis with enoxaparin for prevention of PA-VTE. We report a low rate of breakthrough VTE in women, the majority of whom received standard doses of enoxaparin. High rates of postpartum hemorrhage are reported in our cohort. Our data do not strongly support a move to increase doses of thromboprophylaxis for prevention of PA-VTE and raise the possibility that higher doses may increase bleeding complications and limit women's access to neuraxial analgesia/anesthesia. Background: Low-molecular-weight heparin is used to prevent pregnancy-associated venous thromboembolism (PA-VTE), but there are limited data to inform which women require thromboprophylaxis in pregnancy and debate about which low-molecular-weight heparin dose is effective and safe. Aims: To evaluate the efficacy and rate of complications using enoxaparin for thromboprophylaxis in a cohort of women at risk of PA-VTE managed between 1999 and 2014 at National Women's Hospital, a tertiary obstetric referral center in Auckland, New Zealand. Methods: A retrospective, observational study of women who received thromboprophylaxis with enoxaparin for prevention of PA-VTE while under the care of the obstetric or maternal fetal medicine team. Results: A total of 172 pregnancies in 123 women were identified. A single daily dose of 40 mg enoxaparin was used in 94.8% of pregnancies. Two breakthrough PA-VTEs occurred (1.2% [95% confidence interval, 0.32-4.14]). Postpartum hemorrhage ≥500 mL was reported in 36.6% of births and postpartum hemorrhage ≥1000 mL in 9.3% of births. Only four women were transfused. Neuraxial analgesia/anesthesia was used in 52.4% of births, including 39.6% of vaginal births. Conclusion: Use of standard doses enoxaparin thromboprophylaxis in our cohort was effective at preventing PA-VTE. Neuraxial analgesia/anesthesia was used frequently during labor and birth;, using higher doses of enoxaparin may limit access to this. Postpartum hemorrhage was common and higher doses of thromboprophylaxis may increase obstetric bleeding complications. These data do not suggest an urgent need to consider higher doses of enoxaparin for thromboprophylaxis in this clinical setting.