Salazar‐Ortiz 2016.

Study characteristics
Methods	Randomised controlled trial Duration and location of the trial: prospective trial, randomised, simple, comparative, carried out in patients with infertility for PCOS treated at the Women's Hospital in Mexico City between October 1, 2014 and March 31, 2015.
Participants	Inclusion criteria: women with infertility, diagnosed with PCOS using criteria of the 2003 Rotterdam consensus: 1) oligo‐ovulation, 2) clinical signs or biochemicals of hyperandrogenism, 3) ovary polycystic to transvaginal ultrasound, with establishment of the diagnosis with two of these three criteria; age between 18 and 39 years, with a infertility period more or less greater than 2 years; FSH concentrations ≤ 12 U/L and serum prolactin within normal limits in the early follicular phase, TSH and T4 in normal parameters; patients examined by ultrasound, laparoscopy and hysteroscopy to rule out anatomical alterations before treatment. Exclusion criteria: coexistence of some other added disease, a residual follicle at the time of the endovaginal ultrasound on day 3 of the menstrual cycle. In patients with previous treatment with CC wait 2 months without treatment before starting the cycle with letrozole, to eliminate any after‐treatment effects. Number of centres: single centre Number of women randomised: not clear how many initially randomised Number of women analysed: 24, 12 in each group Number of withdrawals/exclusions/loss to follow‐up and reasons: not reported Age (y): not reported per group BMI (kg/m²): not reported Duration of infertility (y): not reported per group Country: Mexico
Interventions	Group A: patients administered letrozole, oral, 2.5 mg per day, for 5 days, from the third day of the spontaneous menstrual cycle or induced with progesterone. Group B: patients received CC, 100 mg daily for 5 days, starting on the third day of the menstrual cycle.
Outcomes	Clinical pregnancy (confirmed by ultrasound 6 weeks after insemination), endometrial thickness, size of follicles, number of follicles
Notes	Ethical approval: yes, the necessary ethical approval was taken from Institutional Review Board to conduct this trial. Informed consent: yes, the participants were counselled, and informed consent was taken before randomisation. Source of funding: quote: “Source of support: Nil, Conflict of interest: None declared.” Power calculation: none
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Patient groups were determined randomly, with random sampling
Allocation concealment (selection bias)	Unclear risk	Not reported
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Not reported
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Not reported
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	No flow chart available, not reported how many initially randomised
Selective reporting (reporting bias)	Low risk	All outcomes reported
Other bias	High risk	Very small sample size, methodology not sufficiently described