Liu 2015.

Study characteristics
Methods	Randomised controlled clinical trial Duration and location of the trial: not stated
Participants	Inclusion criteria: quote: "the women were diagnosed with PCOS based on the Revised 2003 Consensus Diagnostic Criteria for PCOS. Clomiphene resistance, i.e. failure to ovulate following 100 mg CC for 5 days for at least three cycles; patent fallopian tubes, confirmed by hysterosalpingography or hysteroscopic diagnosis; normal semen analysis parameters of the patients' spouses according to the modified criteria of the World Health Organization (14); normal serum prolactin, thyroid stimulating hormone and 17‑OH progesterone; no systemic disease; no gonadotropin or other hormonal drug treatment during the preceding 3 months; normal blood count and blood chemistry, including glutamic‑pyruvic transaminase, glutamic‑oxaloacetic transaminase, urea nitrogen, creatinine, glucose and urine analysis. The semen of the patients' spouses was tested to strengthen the comparability between the two groups. During the period of treatment, all patients were requested to follow a normal diet and rest regime and to avoid intense physical activities in any form and mental stress and fatigue." Exclusion criteria: infertility induced by reasons other than PCOS; uterine cavity lesions or ovarian cyst; > 40 years old; BMI > 26 kg/m2; contraindications to general anaesthesia; history of pelvic surgery; other endocrine diseases; or a history of liver or kidney disease Number of women randomised: 141 women were randomly assigned, 71 to group A (letrozole) and 70 to group B (LOD) Number of women analysed: all women randomised were also analysed Number of withdrawals/exclusions/loss to follow‐up and reasons: none Number of centres: single‐centre trial Age (y): letrozole group 29.5 ± 3.3, LOD group 28.1 ±3.6 BMI (kg/m²): letrozole group 22.5 ± 1.5, LOD group 22.4 ± 2.1 Duration of infertility (y): letrozole group 3.4 ± 0.4, LOD group 3.2 ± 0.7 Country: China
Interventions	Group A: quote: "In group A, 2.5 mg LE oral tablets (Adooq Bioscience, Nanjing, China) were administered on the fifth day of menses and then every day for 5 days. Treatment was repeated for up to six cycles if the patient failed to conceive." Group B: quote: "In group B, laparoscopy was performed under intravenous general anaesthesia (Diprivan; AstraZeneca S.p.A., Rome, Italy) with the patient in a supine position. A 5‑mm incision was made in the navel, through which a long sheath punctured into the abdominal cavity, and the inflatable pneumoperitoneum (Guangxi University, Yuannan, China) was placed. Another two 5‑mm incisions were made on the right and left lower abdomen and the surgical instruments were inserted into the abdominal cavity. The patient was adjusted into a position with the head high up, the pelvic organs were exposed and a comprehensive exploration of the pelvic organs was made, focusing on the structure and position of the adjacent organs of the bilateral ovaries. Once immobilized, each ovary was cauterized at 4‑6 points, each for 4 sec at 40 W, at a depth of 7‑8 mm and a diameter of 3‑5 mm, using a monopolar electrosurgical needle (Kirgen Co., Shanghai, China), according to the size of each ovary. Following cauterization, a bilateral tubal hydrotubation with methylene blue was performed. During the procedure, small pieces of the ovaries were obtained for pathological analysis. The pelvis was irrigated using physiological saline. Ringer's solution (ZiQi Bioscience, Shanghai, China) plus dexamethasone was added into the abdominal cavity to avoid adhesion. The total duration of the procedure, as well as any intra‑operative or post‑operative complications, was noted. The patients were followed‑up for 6 months after the procedure."
Outcomes	Live birth rate, OHSS, clinical pregnancy was defined by a foetal heart beat monitored by ultrasound at 6 weeks of gestation. Biochemical pregnancy was considered when hCG was > 2.5 mIU/mL in the absence of menstruation. Ovulation rate, endometrial thickness in mm, synchronous cycles, mean follicular diameter, spontaneous abortion rate, multiple pregnancy rate
Notes	Ethical approval: this trial was approved by Tongji Hospital Research Ethics Committee (Shanghai, China) Informed consent: all participants provided informed consent prior to inclusion in the trial. Source of funding: the present trial was supported by the Shanghai Natural Science Foundation (grant no. 12ZR1434200). Power calculation: none reported
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "The women were randomly allocated into the either the letrozole or LOD group (groups A and B, respectively)."
Allocation concealment (selection bias)	Unclear risk	Not reported
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Quote: "Once the patients had been allocated to one of the two groups, the treatment was revealed to the investigator; however, the doctor responsible for performing the transvaginal ultrasound follow‑up assessment was blinded to the treatment groups."
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Quote: "Once the patients had been allocated to one of the two groups, the treatment was revealed to the investigator; however, the doctor responsible for performing the transvaginal ultrasound follow‑up assessment was blinded to the treatment groups."
Incomplete outcome data (attrition bias) All outcomes	Low risk	All women randomised were also analysed
Selective reporting (reporting bias)	Unclear risk	Live birth and spontaneous abortion were reported as outcomes, but not prespecified in the methods
Other bias	Unclear risk	None