Impact of early versus late artificial rupture of membranes during oxytocin induction of labour on the incidence of chorioamnionitis: a randomised controlled trial (ARM trial).

Abstract

Background: The approach to induction of labour differs internationally, with timing of amniotomy being controversial. Some institutions favour performing artificial rupture of membranes prior to commencement of oxytocin infusion, with the belief that the labour will progress more efficiently. In other institutions, the approach recommended is for oxytocin infusion with intact amniotic membranes until the person has reached the active phase of labour, citing risk of infection with early amniotomy. Current evidence is inconclusive. We are performing a randomised controlled trial assessing whether delaying amniotomy until the active phase of labour can decrease the rate of chorioamnionitis.

Methods: This is a randomised controlled trial at a single centre in New Zealand. Pregnant people undergoing induction of labour at ≥ 37 weeks gestational age with intact membranes and a singleton gestation are eligible for the trial. Participants are randomised to 'Early' amniotomy, at the commencement of oxytocin infusion, or to 'Late' amniotomy, when they have reached a cervical dilation of 6 or more centimetres or when they have been receiving oxytocin infusion for 12 h. The primary outcome of the trial is chorioamnionitis. To detect a decrease in chorioamnionitis from 9 to 3% with a power of 80% and a 95% CI, we will require 488 participants in total, randomised in a 1:1 ratio.

Discussion: If delaying amniotomy reduces the rate of chorioamnionitis, this is important to inform future practice. Chorioamnionitis entails risk to both the pregnant person and the fetus and is an important contributor to neonatal sepsis, neonatal intensive care unit admission, maternal sepsis, caesarean, wound infection and postoperative infective complications. Conversely, if the rate of chorioamnionitis is not affected by timing of amniotomy, this will allow for safe individualization of care.

Trial registration: The trial is registered on the Australian and New Zealand Clinical Trials Registry, anzctr.org.au. Full registry title is 'Impact of early versus late artificial rupture of membranes during oxytocin induction of labour on the incidence of chorioamnionitis: A randomised controlled trial'.

Trial id: ACTRN12621000405819. Date registered 14 April 2021.