Tan 2015.

Study characteristics
Methods	RCT
Participants	Inclusion criteria: pregnant women aged 21 to 40 years old with a singleton pregnancy with no major fetal anomaly who were suitable for vaginal delivery and scheduled for a planned IOL at 37‐41 + 6 weeks of gestation. Exclusion criteria: spontaneous labour, had a cervical dilatation of 3 cm or more, confirmed rupture of membrane, had abnormal cardiotocogram, a scarred uterus such as previous CS, malpresentation in labour, or if CS delivery was indicated
Interventions	1. Double balloon (80 mL, balloon started with 40 mL, every following hour 20 mL inserted until 80 mL total), max 12 hours (N = 31) 2. PG 3 mg tablet, repeat once after 6 hours (N = 54) If not in labour or AROM possible after 12 hours, further management by local physician.
Outcomes	Not clearly mentioned in method section
Notes	Setting: tertiary referral maternity unit in Singapore. Study period: not reported Funding: double balloons provided by Cook Medica Declarations of interest: none declared
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Shuffling of 150 envelopes with equal numbers of chance for intervention or control, labelled sequentially
Allocation concealment (selection bias)	Low risk	Sealed envelope, next allocated number of envelope
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	High risk	ITT not described, seems per protocol as woman in pain and breech during labour were excluded; no missing data described
Selective reporting (reporting bias)	Unclear risk	No pre specified outcomes reported, so cannot be judged
Other bias	Low risk	No other bias detected