Study	Reason for exclusion
Cheng 2010	This randomised pilot study was performed to assess whether the effect of coadministration of metformin, CC and hMG was superior to that of CC plus hMG in women with CC‐resistant PCOS. Ovulation induction was provided with CC and hMG together. No woman was treated with hMG solely.
de Leo 1999	Two cycles of FSH stimulation, then metformin for 1 month before a third treatment cycle vs treatment with 1500 mg of metformin/d for at least 1 month before a single cycle of FSH stimulation. All cycles of FSH were compared with 1 cycle of metformin in a relatively unfavourable group of women without pregnancy after 2 cycles of ovulation induction.
Raffone 2010	Women were randomly treated with metformin 1500 mg/d orally or 4 grams myo‐inositol. No comparison was made vs placebo or no treatment.
Shihibara 2007	This is a retrospective, non‐randomised comparison between ovulation induction with gonadotrophin, with and without metformin.

CC: clomiphene citrate.

FSH: follicle‐stimulating hormone.

hMG: human menopausal gonadotropin.

PCOS: polycystic ovary syndrome.