Asadollahpour 2015.

Methods	Country: Iran RCT Three study groups. Randomisation method not fully described No evidence of allocation concealment Blinding of personnel delivering the intervention unclear Blinding of outcome assessor unclear
Participants	Preterm infants from 26 to 32 weeks of gestational age fed through a tube with birth weight 1000 to 2000 grams NNS intervention group: N = 11 (6 male/5 female), GA 30.18 ± 1.77 weeks, birth weight 1406.36 grams Prefeeding oral stimulation group: N = 10 (5 male/5 female), GA 30.01 ± 1.76, birth weight 1343.01 grams Control group: N = 11 (5 male/6 female), GA 30.29±1.95, birth weight 1393.63 grams
Interventions	NNS intervention: thrice‐daily stroking of the palate for 5 minutes to elicit a suck. This intervention was delivered by a speech and language therapist (SLT) who was 'blinding to research' and was performed through insertion of the SLT's little finger into infant’s oral cavity to gently stroke the hard palate to elicit a suck. NNS stimuli were started during initial 5 minutes of tube feeding and were administered for 10 consecutive days. Protocol same as that described by Harding 2009 Prefeeding oral stimulation intervention: performed by the same SLT. Oral stimulation programme consisted of once‐daily stroking of cheeks, gums and tongue, followed by 3 minutes of non‐nutritive sucking for 15 minutes. Protocol same as that described by Fucile 2002 Control: Group received sham intervention. For this group, the same SLT placed her hands in the incubator without touching the infant for 15 minutes. This was administered for 10 consecutive days
Outcomes	Primary outcome: time to attain independent oral feeding Secondary outcomes: Length of hospital stay Weight gain
Notes	For birth weight, median values provided. Mean or standard deviation had to be calculated. Adverse events not recorded or reported
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Random assignment was performed by 'a simple randomisation method', whereby infants were randomly assigned to NNS (n = 11), prefeeding oral stimulation (n = 10) and control (n = 11) groups. This was not clearly described.
Allocation concealment (selection bias)	High risk	Despite study authors reporting, "This intervention delivered by one speech therapist who was blinding to research", this SLT delivered all interventions and therefore was aware of allocation in all groups.
Blinding of participants and personnel (performance bias) All outcomes	High risk	Same SLT delivered all interventions and sham interventions and was not blinded.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Weight was measured by 'a nurse'. It is unclear whether the same nurse measured all infants, or whether the nurse on duty at the time of weigh in performed the measurements.
Incomplete outcome data (attrition bias) All outcomes	Low risk	All outcomes are reported. No data were missing.
Selective reporting (reporting bias)	Low risk	All of the study’s prespecified outcomes and all expected outcomes of interest to the review were reported.
Other bias	Unclear risk	Information was insufficient to permit judgement. Adverse events were not recorded or reported.