Liu 2017.

Study characteristics
Methods	RCT, 4 arms, 142 randomised Setting: Beijing Obstetrics and Gynecology Hospital, China ‐ one centre Recruitment period: February 2012 to November 2014
Participants	Criteria related to previous IVF failure: yes, patients were undergoing first IVF cycle Inclusion criteria: infertile women indicated for IVF treatment; ≤40 years of age; a normal uterine cavity demonstrated by saline infusion sonogram; basal follicle stimulating hormone (bFSH) <12 IU/L Exclusion criteria: endometrium with polyp or fibroid; hydrosalpinx; endometriosis.
Interventions	Study group: for patients in proliferative phase group, endometrial injury was performed between cycle day 10–12. For patients in luteal phase group, endometrial injury was performed 7–9 days after ovulation. The endometrial injury procedure was performed in a standard approach using a pipelle Control group: pipelle catheter inserted through the cervix but no injury was performed to the endometrium (on either cycle days 10‐12 or 7‐9 after ovulation)
Outcomes	Reported in paper: live birth, clinical pregnancy, multiple pregnancy, miscarriage (provided in paper but numbers do not match the difference between live birth and clinical pregnancy, therefore miscarriage calculated based on this difference instead), pain, bleeding Obtained by author correspondence: ‐
Notes	Trial registration: ChiCTR‐IOR‐17011506 (registered May 2017, registered retrospectively) Additional concerns and comments: the outcomes of all clinical pregnancies are not known, for example there are 29 clinical pregnancies in the intervention group and 1 miscarriage, 1 ectopic and 25 live births; there is no description of the fate of the other two pregnancies. Additionally, there are two ectopics in total reported in Table 2 but only one in Table 4 ‐ however only small numbers are involved. Funding: the study was supported by the National Natural Science Foundation of China (81471520), Beijing Natural Science Foundation Project (5122015), and Project Training High‐Level Medical Technical Personnel in the Health System in Beijing (2014–3‐075). Author correspondence: attempted but no response received (yingliubj@hotmail.com) Publication: full‐text.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "table of random numbers" was used
Allocation concealment (selection bias)	Unclear risk	No description
Blinding of participants and personnel (performance bias) All outcomes	Low risk	A sham procedure was implemented which is considered likely to blind participants
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Subjective outcome of pain reported and participants were blind to their trial allocation
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	There appears to be no attrition, however the paper states that all randomised women underwent embryo transfer, which seems unlikely for all 142 women. It is possible that some women were excluded.
Selective reporting (reporting bias)	Low risk	Retrospective registration however live birth and adverse events reported
Other bias	High risk	Trial registered retrospectively. Additionally, the outcome of some pregnancies are not accounted for which questions the accuracy of the data.