Preventing Postpartum Venous Thromboembolism With Low-Molecular-Weight Heparin: The PP-HEP Pilot Randomised Controlled Trial

Objective: Uncertainty surrounds the risk-benefit of low-molecular-weight heparin to prevent postpartum venous thromboembolism (VTE). Data from randomised clinical trials (RCT) are critically needed, but recent feasibility studies in North America yielded low participation rates, with <1 enrolment per month per centre. Our aim was to assess the feasibility of a trial of postpartum short-term enoxaparin in Europe. Design: Pragmatic, open-label pilot randomised controlled trial (RCT). Setting: Swiss tertiary hospital. Population: Postpartum women, within 48 h of delivery, deemed at intermediate risk of VTE with at least one major risk factor (morbid obesity, thrombophilia, emergency caesarean section, pre-eclampsia, preterm delivery, intrauterine growth restriction or systemic peripartum infection) and/or at least two minor risk factors. Methods: Participants were randomised to enoxaparin 40-60 mg once daily for 10 days or no treatment, with a 90-day follow-up. Main Outcome Measures: Participation rate and study acceptance (randomised participants among women in whom informed consent was sought). Results: Recruitment was open for 25 weeks in 2022. Among 1504 postpartum women, 480 were eligible and 77 were randomised. The recruitment rate was 3.1 per week (13.3 per month) and the study acceptance was 23.8%. At 3 months, there was no VTE event, but one major, one nonmajor obstetrical bleeding and one surgical site complication, all in the enoxaparin group. Conclusions: This pilot RCT of postpartum thromboprophylaxis set in Switzerland yielded greater participation rate and acceptance than previous attempts in North America. It calls for a large, international, collaborative trial to guide this important clinical decision. Trial Registration identifier: NCT05878899 and NCT04153760.