OC 25.4 - Preventing postpartum venous thromboembolism with low-molecular-weight heparin: a feasibility randomized controlled trial

Background: Much uncertainty surrounds the risk-benefit of low-molecular-weight heparin to prevent postpartum venous thromboembolism (VTE). Data from randomized clinical trials (RCT) are critically needed, but recent feasibility studies in North America yielded low participation rates, which are not compatible with the large required sample size.

Aims: to estimate the recruitment rate and proportion of participation to a pragmatic, open-label RCT of short-term enoxaparin in the postpartum period.

Methods: This RCT was set in a Swiss tertiary hospital. Inclusion criteria were postpartum women, within 48h of delivery, deemed at intermediate risk of VTE, with at least 1 major risk factor (morbid obesity, thrombophilia, emergency c-section, pre-eclampsia, preterm delivery, intra-uterine growth restriction or systemic peripartum infection) and/or at least 2 minor risk factors (>35years, obesity, elective c-section, postpartum hemorrhage, current smoking and recent immobility). Participants were randomized to enoxaparin 40-60mg o.d. for 10 days or no treatment, with a 3-month follow-up for thrombotic, bleeding and obstetrical outcomes. Approval from the local ethics committee and individual informed consent were obtained.

Results: Recruitment was open for 25 weeks, from May until November 2022. We screened 1504 postpartum women, of which 480 were eligible and 323 were approached by a study investigator. Seventy-seven women (24%) agreed to participate. Fear of injection was stated as the main reason for non-participation (54%). The recruitment rate was 3.1 participant per week (12.8 per month). The most common major risk factors for VTE were an emergency c-section (44%) and a morbid pre-pregnancy obesity (18%). Study follow-up is ongoing.

Conclusion(s): This pilot RCT of postpartum thromboprophylaxis set in Europe yields a greater participation rate and proportion of study enrollment than previous attempts in North America. It calls for a large, international, collaborative pragmatic trial to guide this important clinical decision and recommandations.