Mehrangiz 2004.

Methods	Randomised.
Participants	100 women with uncomplicated term pregnancies in established early labour. 42% of women were primigravidae. Women with uteroplacental insufficiency, diabetes, gestational hypertension, malpresentation, chronic hypertension were excluded. Selected patients were at 4‐5 cm cervical dilatation and had contractions. The visual pain scale was performed and the patients with score 8‐10 were included in the study.
Interventions	Group 1 ‐ Promethazine 25 mg intramuscularly every 3 hours. Group 2 ‐ PCB and promethazine when needed.
Outcomes	Time onset of analgesia, mean time of pain free interval and parity, neonatal outcome, effect on fetal heart rate, degree of pain relief, mean labour progress, the rate of caesarean section, Apgar scores.
Notes	The description of intervention was limited. The solution, concentration and dosage used for PCB were not named in the paper.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	"Randomly divided."
Allocation concealment (selection bias)	Unclear risk	Not described.
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	In the abstract authors mentioned that "double blinding" was performed, however there are no further details.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	In the abstract authors mentioned that "double blinding" was performed, however there are no further details.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Data complete.
Selective reporting (reporting bias)	Low risk	No bias identified.
Other bias	High risk	The description of intervention was limited. The solution, concentration and dosage used for PCB were not named in the paper.