Siebert 2009.

Methods	RCT  Setting: South Africa  Method of randomisation: computer‐generated random numbers Blinding: unblinded  Number randomised: 107
Participants	Summary: metformin and CC vs CC in obese PCOS women Inclusion criteria: PCOS (according to Rotterdam consensus 2003), confirmed tubal patency Exclusion criteria: male factor subfertility  Baseline characteristics of each group: metformin and CC (n = 42) vs CC (n = 48) median  BMI: 30.48, 30.71 median fasting insulin mIU/L: 17.20, 13.6 median fasting glucose 5.00, 5,10 median total testosterone nmol/L: 2.35, 2.00 Dropouts: 17, 10 in metformin + CC group and 7 in CC‐only group
Interventions	Main intervention: metformin 850 mg twice daily  Duration: 6 weeks before and throughout ovulation induction with CC  Co‐interventions: CC 50‐150 mg day 4‐8 for 4 cycles
Outcomes	Primary: none Secondary: ovulation: day‐21 progesterone level (level not stated)
Notes	A single‐centre RCT investigated the benefit of using metformin in CC ovulation induction treatment. ITT was used in our analysis. Participant lost to follow‐up classified as non‐responder; whilst pregnant participants did not attend follow‐up visit (1 in each arm) were classified as responder No units for insulin, glucose and testosterone in the paper
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Computer‐generated random numbers
Allocation concealment (selection bias)	Unclear risk	Not stated
Blinding of participants and personnel (performance bias) All outcomes	High risk	Unblinded
Blinding of outcome assessment (detection bias) All outcomes	High risk	Unblinded
Incomplete outcome data (attrition bias) All outcomes	High risk	Dropouts: no significant difference in the dropout rates, 10 in metformin + CC group and 7 in CC‐only group; no reason for dropout
Selective reporting (reporting bias)	Unclear risk	Insufficient information in the study
Other bias	Low risk	No evidence of other bias