Methods	RCT 2-arm parallel group design.
Participants	Argentina: 2 hospitals. 310 women of mixed parity, in labour 37-42 weeks’ gestation with cervix 4-6 cm dilated, cephalic presentation and requiring analgesia Exclusions: maternal medical condition, evidence of fetal distress, previous caesarean section
Interventions	Experimental: IM nalbuphine 20 mg, single dose (N = 152). Control: IM pethidine 100 mg, single dose (N = 158).
Outcomes	Primary: neonatal Apgar score < 7 at 1 min. Secondary: maternal pain assessed using VAS pre-injection, and 30 and 120 min afterwards (severe pain 75 or >), nausea, vomiting and type of birth. Neonatal side effects: condition over first 24 hrs, admission to neonatal intensive care nursery
Notes	Stratified by hospital.
Risk of bias
Bias	Authors’ judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Computer-generated code.
Allocation concealment (selection bias)	Low risk	Coded ampoules, sealed and prepared by independent pharmacist and identical in appearance
Blinding (performance bias and detection bias) Women	Low risk	Identical ampoules.
Blinding (performance bias and detection bias) Clinical staff	Low risk	Identical ampoules.
Blinding (performance bias and detection bias) Outcome assessor	Unclear risk	Not reported.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Few losses to follow-up.
Selective reporting (reporting bias)	Unclear risk	Not mentioned if women reported pain to their caregiver.
Other bias	Unclear risk	Data analyst unaware of coding. Balanced at baseline.