Metwally 2020.

Study characteristics
Methods	RCT, 2 arms, 1048 randomised Setting: UK, 16 IVF clinics Study period: June 2016 – Oct 2019 (unclear if recruitment period or entire study period)
Participants	Criteria relating to previous IVF failure: yes, women undergoing their first IVF cycle Inclusion criteria: (extracted from protocol) 1. Women expected to be aged between 18 and 37 years (inclusive) at time of egg collection. 2. First‐time IVF with or without ICSI treatment using the antagonist or long protocol only. 3. Expected to receive treatment using fresh embryos. 4. Expected good responders to treatment, with: a. Ovulatory menstrual cycle b. Normal uterine cavity c. Expected good ovarian reserve Exclusion criteria: (extracted from protocol) 1. Previous trauma/surgery to the endometrium (e.g. resection of submucous fibroid, intrauterine adhesions). 2. Body mass index (BMI) of 35 kg/m2 or greater. 3. Known grade 4 (severe) endometriosis. 4. Currently participating in any other fertility study involving medical/surgical intervention. 5. Expected to receive protocols other than antagonist or long (e.g. ultra long protocol). 6. An endometrial scratch (or similar procedure, e.g. endometrial biopsy for the collection of natural killer cells) is planned. 7. Previously randomised into this trial.
Interventions	Study group: Endometrial Scratch (ES) performed in the mid luteal phase prior to IVF/ICSI. The procedure is performed with a pipelle or similar. Control group: no procedure
Outcomes	Reported in paper: live birth, clinical pregnancy, miscarriage. Information regarding pain was provided in a box plot during the oral presentation, however it was not possible to determine the mean and SD from this presentation. Obtained from author correspondence: ‐
Notes	Trial registration: ISRCTN23800982 (registered May 2016, registered prospectively) Additional concerns and comments: none Funding: NIHR (UK) Author correspondence: yes, limited correspondence undertaken with Robin Chatters (r.chatters@sheffield.ac.uk) Data reported in the trial abstract was slightly different to that reported in the oral presentation; however the authors did not answer our questions, we therefore used the abstract data. For the same reason, the methodological information relating to the trial was extracted from the supplied study documents (protocol, SAP etc) as the authors did not answer our questions. Publication: abstract only (and oral presentation viewed at ESHRE 2020)
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	The protocol states quote: "The randomisation schedule will be generated by Sheffield CTRU prior to the start of the trial; access to the schedule will be limited only to the trial statistician. The randomisation sequence will be computer generated and stratified by site and protocol (antagonist or long protocol). Random permuted blocks of variable size will be used to ensure enough participants are allocated evenly to each arm of the trial at each site"
Allocation concealment (selection bias)	Low risk	The protocol states "Research staff at recruiting centres will be unable to access the randomisation sequence and will use a web‐based computer system with restricted access rights to enter participant details; randomisation outcome will then be revealed"
Blinding of participants and personnel (performance bias) All outcomes	High risk	No blinding was used. Also it was observed that a higher proportion of women in the endometrial injury arm underwent double embryo transfer compared to women in the control arm.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	The outcome of pain during the procedure were self‐reported by participants who were not blind to their treatment allocation, however this data was not available for inclusion in this review.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	No information available about the numbers of women lost to follow‐up or withdrawn
Selective reporting (reporting bias)	Unclear risk	Although the study protocol was registered prospectively, only an abstract is available and therefore it is not possible to assess whether all registered outcomes have been/will be reported
Other bias	Low risk	Only an abstract is available and the trial team refused to answer our questions by email, however sufficient information was available and therefore this is not seen to constitute a high risk of bias.