Berntsen 2020.

Study characteristics
Methods	RCT, 2 arms, 229 randomised Setting: Denmark, two public fertility clinics (only participants from one included in the analysis) Recruitment period: 2013 ‐ 2018 (months not provided, recruitment period stated as 5 years)
Participants	Criteria related to previous IVF failure: yes, minimum one previous failed cycle Inclusion criteria: women were eligible if they had minimum one previous failed cycle and were planned to undergo their next IVF or ICSI cycle with fresh embryo transfer. Women between 18 and 40 years of age (both ages included) were included. Exclusion criteria: freeze‐all cycles and frozen embryo transfers (FET) were excluded. Further, women were excluded if they had (i) BMI 35, (ii) known intrauterine pathology as cause of infertility, (iii) significant systemic disorders, (iv) ongoing infection (reproductive tract or systemic), (v) intrauterine abnormalities diagnosed during the trial hysteroscopy, or if they became spontaneously pregnant during the trial
Interventions	Study group: hysteroscopy and endometrial biopsy in the follicular phase of the preceding cycle, performed using 7 F forceps Control group: no procedure
Outcomes	Reported in paper: live birth, clinical pregnancy, miscarriage (defined as loss of a clinical pregnancy before 24 weeks, authors confirmed clinical pregnancy was defined as a positive pregnancy test) Obtained by author correspondence: the authors confirmed they did not measure pain or bleeding following the procedure.
Notes	Trial registration: NCT01743391 (registered Dec 2012, prospective registration) Additional concerns and comments: none Funding: Paper states quote: "No specific funding was sought for this study" Author correspondence: yes, undertaken with kristine.juul.hare.01@regionh.dk and sine.berntsen.01@regionh.dk. Publication: full‐text. This poster was first discovered at the NFOG conference in Odense, 2018 (Poster ID ES27‐0205), however there was no useable data in available in the poster.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	The paper states quote: "participants were computer randomised using an online, third‐party randomisation system and assigned...Randomisation was performed as a simple randomisation in a 1:1 ratio without using block randomisation or stratification...One physician was responsible for computer randomising all participants."
Allocation concealment (selection bias)	Low risk	A substantial imbalance in recruitment to each arm was observed (122 versus 107). No description provided in the paper however the authors informed us that quote:"The randomisation was performed in the program SAS. We used a logarithm where a physician (Dr Hare) typed the date of birth of the patient, this together with exact time – date, hour, minute and second, generated a number <1. All <0.5 were in group 1 (ESI group) all >0.5 were controls. All participants were only recruited/randomised once." Although it appears possible that the physician could have randomised women a second time to retrieve a different allocation, the authors also confirmed that the randomisation registered the patients Danish social security number and assigned a number based on the chronology of randomisation ‐ at the end of the study they checked that each patients social security number was only assigned a single randomisation event.
Blinding of participants and personnel (performance bias) All outcomes	High risk	Trial was not blinded quote:"This was a randomised controlled trial (RCT) with no blinding of participants, investigators or health care personnel”
Blinding of outcome assessment (detection bias) All outcomes	Low risk	No subjective outcomes reported
Incomplete outcome data (attrition bias) All outcomes	High risk	It is stated that a number of women were excluded post‐randomisation quote:"Freeze‐all cycles and frozen embryo transfers (FET) were excluded. Further, women were excluded if they had... intrauterine abnormalities diagnosed during the trial hysteroscopy, or if they became spontaneously pregnant during the trial“ The authors confirmed that these exclusions are all those documented within Figure 1. In total, there were 14 exclusions in the scratch arm and 3 in the control arm. This imbalance in exclusions may have impacted the analyses. Additionally, data from one of the two included centres was completely omitted due to clinic closure quote:"Data reported and analysed in this article are exclusively from the main centre at Copenhagen University Hospital, Hvidovre as the other fertility clinic (Holbaek) closed down during the study and the patients were lost to follow‐up" and these are the 28 women (15 and 13) described as excluded in Figure 1.
Selective reporting (reporting bias)	Low risk	The trial was registered prospectively, and the listed outcomes are reported.
Other bias	Low risk	The trial was terminated early due to lack of funding, however this is not considered to cause bias