Does metformin prolong pregnancy in preterm pre-eclampsia? A study protocol for a South African, hospital-based double-blind, randomised, placebo-controlled trial

Introduction Preterm pre-eclampsia is a leading cause of maternal morbidity and mortality. The Pre-eclampsia Intervention 2 (PI 2) trial suggested that metformin sustained release (XR) may prolong gestation by a week in pregnant women undergoing expectant management (7.6 days, geometric mean ratio 1.39, 95% CI 0.99 to 1.95; p=0.057). These findings should be confirmed with a larger sample size, and we need to know if such a prolongation improves neonatal outcome. Here, we describe the protocol for such a follow-up trial.Methods The PI 3 trial is a phase III, intention-to-treat, double-blind, placebo-controlled randomised clinical trial to assess if metformin XR can prolong gestation and improve neonatal outcomes in women undergoing expectant management for preterm pre-eclampsia. We will recruit women who are between 26+0 and 31+6 weeks pregnant. Women will be randomised to receive either 3 g metformin XR or an identical placebo in divided daily doses. The primary outcome is prolongation of pregnancy. Secondary outcomes are neonatal birth weight and length of neonatal care admission (an indicator of neonatal health at birth). All other outcomes will be exploratory. We will record tolerability and adverse events. We plan a sample size of 500 participants to be powered for the primary and secondary outcomes.Ethics and dissemination PI 3 has ethical approval (Health Research Ethics Committee 2, Stellenbosch University, Protocol number M21/03/007, Project ID 21639, Federal Wide Assurance Number 00001372, Institutional Review Board Number IRB0005239), and is registered with the Pan African Clinical Trial Registry (PACTR202104532026017) and the South African Medicine Control Council (20211211). Data will be presented at international conferences and published in peer-reviewed journals.Trial registration number PACTR202104532026017)