Hemminki 1986.

Methods	Randomised controlled trial. Randomisation was by means of sealed envelopes in blocks of 10, stratified for gravidity. Women were randomised during the first stage of labour.
Participants	175 women, Kainuu Central Hospital, Kainuu, Finland. 88 study participants. 87 control participants. All women had reached 35 weeks completed gestation. Singleton pregnancies. No contra‐indications for normal vaginal birth. Vertex presentation. No medical, surgical or obstetric complications.
Interventions	Study group: 88 women were randomised during the first stage of labour to use a birth chair. The mean cervical dilatation when transferred to the chair was 8.8 cm. The chair was made locally and was normally maintained with the back 60º to 70º from the horizontal. 12 women did not deliver in the chair. Control group: 87 women lay on their backs, propped up < 45º from the horizontal.
Outcomes	There were no statistically significant differences between groups for maternal age, gestation, gravidity, birthweight and Apgar scores. Method of birth.
Notes	Data not in a usable format.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Randomisation was in blocks of 10, stratified for gravidity.
Allocation concealment (selection bias)	Unclear risk	Sealed envelopes. No further information provided.
Blinding of participants and personnel (performance bias) All outcomes	High risk	Participants and personnel aware of allocation.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Insufficient information provided.
Incomplete outcome data (attrition bias) All outcomes	High risk	Missing data for mothers' preference in the next birth for both groups. In bed group, position in this birth missing for 16 women. These were not addressed.
Selective reporting (reporting bias)	Low risk	All outcomes reported.
Other bias	Low risk	No other bias found.