Methods	RCT, 2-arm parallel groups.
Participants	Setting: UK hospital. 46 women (20 primiparous and 14 multiparous women included in the analyses). Uncomplicated pregnancy Exclusions: first stage of labour > 12 hr, second stage > 1 hr, body weight <45 kg, multiple pregnancy, non-vertex presentation, preterm or postmature labour, previous caesarean section, birth weight outside the 5th and 95th centiles for gestational age, congenital fetal abnormality
Interventions	Experimental: IM meptazinol 1.5 mg/kg body weight plus 10 mg metoclopramide hydrochloride (N = 17) Control: IM pethidine 1.5 mg/kg body weight plus 10 mg metoclopramide hydrochloride (N = 17)
Outcomes	Neonatal acid-base balance. Maternal pH pre injection, repeated at head crowning, neonatal pH at 10 and 60 min PN
Notes	If additional analgesia required opioid repeated > 3 hrly. Actual dose received by women not reported
Risk of bias
Bias	Authors’ judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Not reported.
Allocation concealment (selection bias)	Unclear risk	Not reported.
Blinding (performance bias and detection bias) Women	Unclear risk	States double blind but not described.
Blinding (performance bias and detection bias) Clinical staff	Unclear risk	States double blind but not described.
Blinding (performance bias and detection bias) Outcome assessor	Unclear risk	States double blind but not described.
Incomplete outcome data (attrition bias) All outcomes	High risk	12 women excluded from analysis, reasons for all exclusions not explained
Selective reporting (reporting bias)	High risk	Reasons why some participant data excluded not explained. 3/12 excluded because problem with pH analyser (meptazinol group)
Other bias	Low risk	No baseline imbalances.