Methods	RCT.
Participants	600 nulliparous, low-income, under-insured pregnant women (300 doula group, 300 control group) booked for delivery at a hospital in New Jersey, USA were enrolled between 12 and 38 weeks’ gestation. They were considered low risk, with no contraindications to labour and had a female friend or relative willing to act as their lay doula. The doula was in addition to support people of their own choosing
Interventions	Intervention: continuous support by a female friend or relative who had had 2, 2-hour sessions about labour support. The training sessions were conducted for nearly all of the lay caregivers when the participants were 34-36 weeks’ gestation Control group: support people of their own choosing.
Outcomes	Labour length, epidural analgesia, oxytocin augmentation, cervical dilation at epidural insertion, length of second stage labour, caesarean birth, 1-min Apgar score > 6, 5-min Apgar score > 6
Notes	Epidural analgesia was available and EFM was used routinely.
Risk of bias
Bias	Authors’ judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	‘Computer generated randomization scheme.’
Allocation concealment (selection bias)	Low risk	Consecutively-numbered, sealed opaque envelopes contained treatment assignments. After obtaining consent, a research assistant opened the next envelope. It was unclear whether the research assistant enrolling the woman was the same one that opened the envelope
Blinding (performance bias and detection bias) All outcomes	High risk	Medical record abstraction was done by the author who was not blinded. The 6-week questionnaire data collection was not blinded
Incomplete outcome data (attrition bias) All outcomes	High risk	Medical record information was completed for 97.7% of the sample (82.3% in the intervention group and 94.3% in the control group). The differential rates are due to withdrawals from the intervention group for doula related reasons (incomplete training and not being present during labour). The 6-week questionnaire was completed for 82.3% of the sample. Only those women included in the study at delivery had the opportunity to complete the questionnaire and thus the differential completion rate between groups remained (76.3% in the intervention group and 88.3% in the control group). The differential withdrawals could introduce selection bias
Selective reporting (reporting bias)	Low risk	All outcomes were reported.
Other bias	Unclear risk	The training of the doulas giving the intervention was done by the research assistant, who was herself a doula. This same research assistant enrolled all study participants