Thiery 1981.

Study characteristics
Methods	RCT. Concealment of allocation by envelopes.
Participants	Singleton vertex term pregnancies. Favourable cervix (BS > 5).
Interventions	Foley catheter with a balloon inflated with 30 mL saline and PGE2 0.5 mg extra‐amniotic (48 women); PGE2 0.5 mg extra‐amniotic (43 women); amniotomy and oxytocin if needed (52 women).
Outcomes	No outcomes reported.
Notes	No relevant outcomes reported. Setting: Belgium Study period: not reported Funding: received free PGE2. not clear if this gift is related to a pharmaceutical company Declarations of interest: not reported
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Prepared envelopes with numbers
Allocation concealment (selection bias)	Low risk	Concealment of allocation by 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	Low risk	Unclear if ITT was performed, but is reasonable as numbers are equal to randomised numbers), no missing cases or data
Selective reporting (reporting bias)	Low risk	All pre‐specified outcomes reported
Other bias	Low risk	No other bias detected