Adjusting enoxaparin dosage according to anti-FXa levels and pregnancy outcome in thrombophilic women. A randomised controlled trial

Abstract

Women with thrombophilias and previous placenta-mediated pregnancy complications (PMPC) have an increased risk of both recurrent PMPC and venous thromboembolism (VTE) during subsequent pregnancies. We aimed to examine whether enoxaparin dose adjusted according to anti-factor Xa levels compared to a fixed dose would reduce the risk of PMPC in subsequent pregnancies. In a randomised trial, conducted at a single teaching hospital, pregnant women with thrombophilia and previous PMPC were enrolled in a 1:1 ratio to either a fixed dose of 40 mg daily enoxaparin or adjusted dose according to anti-factor Xa plasma levels. The primary outcome was a composite that included any of the following: pregnancy loss after enrollment, pre-eclampsia, birthweight <10th percentile, placental abruption, or VTE. Overall, 144 women were needed to detect a decrease of 20 % in the incidence of the composite outcome among the adjusted dose group. Between 2009 and 2015, 144 women consented; four in the fixed-dose group were excluded. Overall, 66 and 74 in the fixed- and adjusted-dose groups, respectively, were included. Demographic and obstetric characteristics were comparable. Composite outcome occurred in 12 (18.2 %) and 20 (27.0 %) women in the fixed- and adjusted-dose groups, respectively (p=0.24). Gestational age at delivery, preterm births, and birthweights were similar between the two groups. In conclusion, dose of enoxaparin adjusted according to anti-factor Xa levels compared to fixed dose, does not reduce the risk of PMPC recurrence in thrombophilic women.

Trial registration: ClinicalTrials.gov NCT01068795.

Keywords: Anti-factor Xa; low-molecular-weight heparin; placenta-mediated pregnancy complications; thrombophilia.