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. 2017 Aug;15(8):461–470.

Supplementary 1.

Risk of bias assessment for included studies

Risk of Bias Quotations
Syngelaki 2016
Random sequence generation (Selection bias) Low "Eligible women were randomly assigned, in a 1:1 ratio, with the use of computer-generated random numbers, to receive either metformin or placebo."
Allocation concealment (Selection bias) Low "The appearance, size, weight, and taste of the placebo tablets were identical to those of the metformin tablets; both were purchased at full cost from University College London Hospitals NHS Foundation Trust."
Blinding of participants and personnel (Performance bias) Low "Double-blind"
Blinding of outcome assessment (Detection bias) Unclear
Incomplete outcome data (Attrition bias) Low "The analysis was performed according to the intention-to-treat principle"
Selective reporting (Reporting bias) Low All outcomes were reported in a pre-specified protocol.
Other bias Low No other sources of bias could be detected.
Chiswick 2015  
Random sequence generation (Selection bias) Low "We randomly assigned participants (1:1), via a web based computer generated block randomization procedure."
Allocation concealment (Selection bias) Unclear
Blinding of participants and personnel (Performance bias) Low "Double-blind"
Blinding of outcome assessment (Detection bias) Low "Members of the independent Data Monitoring Committee had access to unmasked data reports, but had no contact with study participants."
Incomplete outcome data (Attrition bias) Low "All randomly assigned patients to enter safety and efficacy analysis (ITT)"
Selective reporting (Reporting bias) Low All outcomes were reported in a pre-specified protocol.
Other bias Low No other sources of bias could be detected.