Blumenthal 1990.

Study characteristics
Methods	RCT. Randomisation by drawing a blank envelope from a stack of 50 identical envelopes containing the group allocation.
Participants	Vertex, intact membranes, BS < 5, no previous CS.
Interventions	Dilapan (polyacrilonitrile hydrogel) inserted in the cervix, up to 6 sticks (23 women); Laminaria inserted in the cervix, as many as possible (18 women).
Outcomes	CS.
Notes	Results for a 3rd group of women with favourable cervix treated with oxytocin are presented. These women are not be included in the analysis, as they were not randomly allocated to the intervention. Setting: Michael Reese hospital, Chicago, USA Study period:January 1987 to January 1988 Funding: not reported Declarations of interest: not reported
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Shuffling envelopes
Allocation concealment (selection bias)	Low risk	Women choose from stack of all blank, identical 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	High risk	ITT not reported. no explanation what happened to the rest of the randomised women
Selective reporting (reporting bias)	Low risk	All pre‐specified outcomes reported
Other bias	Low risk	No other bias detected