Methods	Randomisation by consecutively numbered, computer generated random allocation in sealed opaque envelopes. Methodological qualities: selection bias: low risk; adequate concealment at time of randomisation; performance bias: high risk of bias could have been introduced because researcher cannot be blind to group allocation after randomisation; exclusion bias: high risk of bias; bias conclusion: high risk of bias. Where 1 or more criteria are not met may cause plausible bias that seriously weakens confidence in the results
Participants	Academic hospital, Ontario, Canada. Inclusion criteria: gestation > 37 weeks; previous CS included (VBAC); twins included; active labour > 3 cm cervical dilatation; ruptured membranes on entry also eligible. Ambulation, analgesics and anaesthesia were allowed. 800 women were randomised, 15 were withdrawn 8 from study group and 7 from control group. Nearly half (46%) of the women in the study group did NOT use the bath but were still considered experimental subjects with the intent to treat. 41 of the women did not meet eligibility criteria but were still included and results were analysed. Experimental group adds up to 394.
Interventions	Study group: n = 393. The use of a Parker whirlpool hot tub with jets during labour. Bath temperature between 38-39 degrees celsius. Mean total time in tub was 54 minutes. No births in tub Control group: n = 392. No water immersion during labour. Refer to care being provided by assigned nurse, and all had be trained to care for women using immersion, but not clear if this is 1-to-1 second care First stage only.
Outcomes	Maternal outcomes: *use of analgesia/anaesthesia; *augmentation of labour; *presence of meconium-stained liquor; *duration of labour and birth; *mode of delivery. Additional outcomes: maternal age; gravida; cervical dilatation; duration in tub; VBAC.
Notes	Data table 1 incorrect. No response from authors.
Risk of bias
Bias	Authors’ judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Computer generated.
Allocation concealment (selection bias)	Low risk	Consecutively numbered sealed opaque envelopes.
Blinding (performance bias and detection bias) All outcomes	High risk	High risk of bias could have been introduced because women, carers and researcher cannot be blind to group allocation after randomisation due to the nature of the intervention
Incomplete outcome data (attrition bias) All outcomes	Low risk	All participants are accounted for, and 15 withdraws were detailed, as were 41 who did not meet criteria but were recruited. These are small numbers from 800 recruited
Selective reporting (reporting bias)	Low risk	All outcomes mentioned in methods are reported, and seem appropriate for the study and topic
Other bias	Unclear risk	46% of women did not use the water, but that was expected as women had choice, and sample size was planned for this