ABSTRACT
Background: Induction of labor is a commonly performed obstetric intervention. Vaginal prostaglandin E2 (dinoprostone) is the recommended first choice agent in the UK. Mechanical methods of induction are slower to achieve cervical ripening but have a lower risk of adverse effects. Objective: To compare the efficacy, maternal and neonatal safety, and maternal satisfaction of a synthetic osmotic cervical dilator (Dilapan-S) with vaginal prostaglandin E2 (dinoprostone) in cervical ripening for induction of labour. Design: Open-label, multicentre, superiority, randomised controlled trial in four UK National Health Service maternity units. Participants: Eligible participants were women ≥ 16 years of age undergoing induction of labour for a singleton pregnancy, ≥ 37 weeks' gestation with vertex presentation and intact membranes. The trial did not reach its planned sample size of 860 due to restrictions on research during the Covid-19 pandemic. Interventions: Women were randomly assigned to receive Dilapan-S or dinoprostone using a telephone randomisation system minimised by hospital, parity, BMI and maternal age. The induction agent was replaced as required until the cervix was assessed as favourable for labour. Main outcome measures: The primary outcome was failure to achieve vaginal delivery (i.e. caesarean delivery). Secondary outcome measures included maternal and neonatal adverse events. Analysis was by intention-to- treat, adjusting for design variables where possible. Results: Between 19 December 2017 and 26 January 2021, 674 women were enrolled: 337 were randomly assigned to Dilapan-S and 337 to dinoprostone (n = 337). The primary outcome was missing for two women in the dinoprostone group. Failure to achieve vaginal delivery (caesarean section) occurred in 126 women (37.4%) allocated to Dilapan-S, and 115 (34.3%) women allocated to dinoprostone (adjusted risk difference 0.02, 95% confidence interval -0.05 to 0.10). There were similar maternal and neonatal adverse events between the groups. Conclusions: Women undergoing induction of labour with Dilapan-S have similar rates of caesarean section and maternal and neonatal adverse events compared to dinoprostone.