Chen 2016.

Study characteristics
Methods	Randomised controlled trial Duration and location of the trial: quote: "All patients were admitted in our hospital between January 2013 and January 2015, who were not pregnant without contraception for over one year.“
Participants	Inclusion criteria: quote: "all the cases were PCOS infertility patients in line with the PCOS diagnostic criteria of the 2003 Rotterdam Conference, i.e. at least two of the following three were met: 1) ovulation abnormality (sporadic ovulation or no ovulation) occurred after continuous monitoring for two or more natural cycles; 2) the results of B ultrasound showed polycystic ovary; 3) patients had hyperandrogenism or showed clinical manifestations of androgen excess. Through salpingography or hydrotubation under transvaginal B ultrasound and other examinations, all cases were confirmed to have tubal patency on at least one side. The semen of male was normal." Exclusion criteria: quote:"Those with androgen excess caused by other diseases such as adrenal hyperplasia Cushing’s syndrome and androgen‐secreting tumours were excluded. Exclusion criteria: 1) Infertility patients caused by non‐PCOS ovulatory disorder or other factors; 2) patients with history of ovarian surgery or complication with endometriosis or pelvic adhesion; 3) patients complicated with liver, kidney or thyroid dysfunction; 4) patients who did not receive treatment after enrolment according to the established regimen or gave up in the midst of treatment." Number of women randomised: 156 patients, 52 in each group Number of women analysed: 156 patients, 52 in each group Number of withdrawals/exclusions/loss to follow‐up and reasons: none reported Number of centres: single‐centre trial Age (y): letrozole group 26.4 ± 4.2; CC group 27.1 ± 4.7; letrozole + hMG group 27.7 ± 5.2 years BMI (kg/m²): letrozole group 22.4 ± 4.5; CC group 23.4 ± 1.5; letrozole + hMG group 22.6 ± 2.6 years Duration of infertility (y): letrozole group 3.4 ± 1.1; CC group 3.2 ± 0.7; letrozole + hMG group 3.3 ± 1.3 years Country: China
Interventions	Group A (letrozole): the participants orally took 2.5 mg/d‐1 to 5.0 mg/d‐1 letrozole (trade name: Fu Rui, Jiangsu Hengrui Medicine Co, Ltd.) on the 3rd ‐ 5th days of menstrual cycle for 5 consecutive days. Group B (CC group): the participants were orally administered with 50 mg/d‐1 to 100 mg/d‐1 CC (trade name: Fertilan, Codal Synto Pharmaceutical Co, Ltd.) on the 3rd ‐ 5th days of menstrual cycle for 5 consecutive days. Group C(letrozole + hMG group): the participants orally took 2.5 mg/d‐1 to 5.0 mg/d‐1 letrozole on the 3rd ‐ 5th days of menstrual cycle for 5 consecutive days. Starting from the day of oral administration of CC, 75 IU hMG (trade name: Lebaode, Livzon Group Livzon Pharmaceutical Co. Ltd.) was intramuscularly injected every other day for 5 consecutive days.
Outcomes	Primary outcomes: clinical pregnancy, defined as a foetal heart beat visible via transvaginal ultrasound on 30th day after ovulation Secondary outcomes: OHSS, miscarriage (abortion), multiple pregnancy
Notes	Ethical approval: this trial has been approved by the ethics committee of our hospital. Informed consent: written consent has been obtained from all patients. Source of funding: quote: “None” Power calculation: no power calculation was reported.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: “the patients were randomly divided into an LE group, a CC group and an LE + hMG group”
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	Low risk	All participants randomised were also analysed.
Selective reporting (reporting bias)	Low risk	No trial protocol was found, but all outcomes reported were also analysed.
Other bias	Low risk	None