Methods	RCT, 3-arm parallel groups.
Participants	Setting: The Netherlands, Department of Obstetrics and Gynaecology 180 enrolled, 159 completed the study. Inclusion criteria: healthy ASA physical status I or II term parturients in an active stage of labour, with singleton cephalic presentation, without prior administration of opioid analgesics Exclusion criteria: obesity (BMI ≥ 40 kg m−2), opioid allergy, substance abuse history, and high-risk patients (pre-eclampsia, severe asthma, insulin-dependent diabetes mellitus, hepatic insufficiency, or renal failure)
Interventions	Remifentanil, patient controlled IV, 40 μg loading dose, remifentanil 40 μg per bolus with a lockout of 2 min and max dose limit of 1200 μg h−1 Meperidine, patient controlled IV, 49.5 mg loading dose and 5 mg bolus with lockout of 10 min and max dose limit of 200 mg Fentanyl, patient controlled IV, 50 μg loading dose and 20 μg bolus with lockout of 5 min and a max dose limit of 240 μg h−1.
Outcomes	Outcomes: pain scores (VAS) every hour; sedation score (1 awake, 2 sleepy, 3 eyes closed, 4 eyes closed but rousable, 5 unrousable; overall satisfaction on 10-point scale 2 hours after delivery; side effects - nausea, vomiting, itching; Apgar scores at 1, 5 mins; cord blood gas analysis; NACS scores at 15 min and 2 hr after delivery; oxytocin use; instrumental delivery; CS; spontaneous delivery
Notes	“All women received similar instructions on how to use the PCA device: all parturients were instructed to press the bolus button whenever they needed pain relief.”
Risk of bias
Bias	Authors’ judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	“Established using a computer generated random sequence in numbered envelopes.”
Allocation concealment (selection bias)	Low risk	“Study medication was prepared and blinded by hospital pharmacy.”
Blinding (performance bias and detection bias) Women	Unclear risk	Not reported.
Blinding (performance bias and detection bias) Clinical staff	Low risk	“Observants and medical personnel attending to the parturient were unaware of the drug assignment.”
Blinding (performance bias and detection bias) Outcome assessor	Low risk	“with exception of baseline data, all observations and measurements were made by blinded observers.”
Incomplete outcome data (attrition bias) All outcomes	Low risk	180 enrolled, 159 completed the study: 52 R group; 53 M group; 54 F group; 21 excluded because delivered within 1 hour after randomisation Says “Data analysis was per-protocol”.
Selective reporting (reporting bias)	Unclear risk	All outcomes discussed in methods appear to have been reported upon within results. However, the study protocol was not evaluated
Other bias	Low risk	Baseline characteristics similar.