Methods	RCT, 2-arm parallel group design.
Participants	Setting: hospital in USA. 500 women admitted to hospital in labour. Little information provided
Interventions	Experimental: (185 women) alphaprodine (Nisentil), initial dose 40mg IV, subsequent doses IM Control: (210 women) pethidine, initial dose 100 mg IV, subsequent doses IM Both groups received scopolamine. Analgesia was for the first stage of labour, birth was carried out “with rare exception” under “saddle block or pudendal block terminal anesthesia”
Outcomes	Pain relief (rated just before leaving the room for childbirth); side effects and length of labour
Notes
Risk of bias
Bias	Authors’ judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	No information.
Allocation concealment (selection bias)	Low risk	Coded drug containers.
Blinding (performance bias and detection bias) Women	Low risk	Drugs were prepared by pharmacy in coded containers and the codes were not revealed until after birth
Blinding (performance bias and detection bias) Clinical staff	Low risk	Drugs were prepared by pharmacy in coded containers and the codes were not revealed until after birth
Blinding (performance bias and detection bias) Outcome assessor	Low risk	Drugs were prepared by pharmacy in coded containers and the codes were not revealed until after birth
Incomplete outcome data (attrition bias) All outcomes	High risk	500 women were randomised, 55 women received no analgesia and were excluded, 22 women received more than 1 dose of opioid (not necessarily the same drug) and were excluded, 21 women who were in preterm labour or had a CS were excluded and 1 woman was excluded because she was sensitive to study medication. Data available for 395 women (21% attrition)
Selective reporting (reporting bias)	Unclear risk	Unclear.
Other bias	Unclear risk	Study medication was for pain relief in the first stage of labour, most women received a pudendal block for birth so outcomes relating to birth may not be attributable to study medication alone