Hoppe 2016.

Methods	RCT
Participants	Inclusion: ≥ 18 years, singleton, vertex, BS of ≤ 5, < 4 contractions in 10 minutes, category I fetal monitoring. Exclusion: contraindication for vaginal delivery, planned or received exogenous PG administration, unexplained vaginal bleeding, active herpes simplex, previous caesarean delivery, previous attempt at IOL, non‐English speaking
Interventions	Single balloon 18F Foley, 30 mL, traction applied, max 12 hours Double balloon, Cook 80 mL/80 mL, max 12 hours
Outcomes	BS of > 6 at time of catheter removal, change in BS, time from catheter insertion to spontaneous expulsion or removal, mean time from catheter insertion to vaginal delivery, vaginal delivery in 24 hours, the use of pharmacologic methods for further cervical ripening or augmentation of labour, AROM, epidural use, mode of delivery, indications for CS, chorioamnionitis, AS at 5 minutes < 7, meconium, NICU admissions
Notes	Setting: University of Washington Medical Center Labor and Delivery, USA Study period: January 2010 and November 2013 Funding: no funding by Cook Declarations of interest: none declared
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Block randomisation, stratified for parity, not clear how this was done.
Allocation concealment (selection bias)	Low risk	Sequentially‐numbered opaque, sealed envelopes
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Not feasible due to nature of intervention
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Not reported
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	No ITT reported, most likely per protocol, missing data in baseline characteristic, not in outcomes, no cases missing
Selective reporting (reporting bias)	Low risk	All pre‐specified outcome data reported
Other bias	Low risk	No other bias detected