Methods	RCT 2-arm parallel group design.
Participants	Setting: UK hospital. 100 women in labour at term gestation with uncomplicated pregnancy
Interventions	Experimental: Meptazinol 1.8 mg/kg body weight (N = 50). Control: pethidine 1.8 mg/kg body weight (N = 50). All participants received promethazine 12.5 mg with first injection
Outcomes	Primary: newborn effects: Apgar score at 1 and 3 min.
Notes	If additional analgesia required, a repeat injection could be administered 3 hourly 6/50 women from each arm received a second dose at a 3-hourly interval
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 method not described.
Blinding (performance bias and detection bias) Clinical staff	Unclear risk	States double blind but method not described.
Blinding (performance bias and detection bias) Outcome assessor	Unclear risk	States double blind but method not described.
Incomplete outcome data (attrition bias) All outcomes	High risk	5 babies excluded from analysis due to heart defects and fetal distress
Selective reporting (reporting bias)	Unclear risk	Unclear.
Other bias	Unclear risk	Balanced for parity, weight and size of baby at baseline.