Doldi 2006.

Study characteristics
Methods	Generation of the allocation sequence: not reported Allocation concealment method: not reported Blinding method: no blinding Number and reasons for withdrawals: not reported ITT analysis: yes The authors did not provide additional information about allocation concealment and generation of allocation sequence methods. Prospective randomised trial Metformin versus no treatment
Participants	40 PCOS participants were randomised (20 in the metformin group and 20 in the placebo group). Diagnosis of PCOS followed the Rotterdam criteria (ESHRE/ASRM). Exclusion criteria: a) congenital adrenal hyperplasia b) Cushing's syndrome c) androgen‐producing tumours d) hyperprolactinaemia e) thyroid dysfunction f) participant age older than 40 years g) FSH > 12 mIU/mL The causes of infertility were not reported. Participants did not take any ovulation drugs or hormones for at least 3 months prior to the trial.
Interventions	Group A was pretreated for 2 months with metformin 1.5 g/day until embryo transfer day. Protocol for controlled ovarian hyperstimulation: short protocol GnRH‐antagonist (cetrorelix, Cetrotide) with step‐up rec‐FSH (Gonal F ‐ starting dose 150 IU). GnRH‐antagonist, cetrorelix 0.25 mg/day, was started when the leading follicle reached 14 mm in diameter on ultrasound scan and stopped on the day of hCG. Recombinant hCG (Ovitrelle 250 μg) was given when 2 or 3 follicles reached 16 mm in diameter on ultrasound scan. Oocyte retrieval was performed within 36 h of hCG injection. No more than 3 oocytes were fertilised (in accordance with Italian law). Assisted reproductive technology: IVF Embryo transfer: maximum of 3 embryos were transferred per participant on day 2 after oocyte retrieval under abdominal US guidance. Catheter used for transfer: not reported Luteal phase support: progesterone 90 mg (Crinone 8) was given on the day of oocyte retrieval and was continued until menstruation or a positive pregnancy test
Outcomes	Primary outcomes: a) incidence of OHSS Secondary outcomes: a) number of ampoules of rec‐FSH b) oestradiol levels c) cancelled cycles d) number of mature oocytes
Notes	Country of the study: Italy Clinical trial registration number not provided.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Not stated.
Allocation concealment (selection bias)	Unclear risk	Not stated.
Blinding of participants and personnel (performance bias) All outcomes	High risk	No blinding.
Blinding of outcome assessment (detection bias) All outcomes	High risk	No blinding.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Reasons for withdrawals were not reported.
Selective reporting (reporting bias)	Unclear risk	Live birth and clinical pregnancy rates were not assessed.
Other bias	Unclear risk	The causes of infertility were not reported.