van Hoogenhuijze 2020.

Study characteristics
Methods	RCT, 2 arms, 946 randomised Setting: the Netherlands, 8 academic and 24 general hospitals Recruitment period: January 2016 to July 2018
Participants	Criteria related to previous IVF failure: yes, all participants had one previous IVF/ICSI failure Inclusion criteria: women were eligible if they had undergone 1 full IVF/ICSI cycle with at least 1 embryo transfer without achieving a clinical pregnancy and were planning a new fresh IVF/ICSI cycle. Inclusion criteria were regular indication for IVF/ICSI, age between 18‐44 years, primary or secondary infertility and a normal transvaginal ultrasound. Exclusion criteria: endometriosis grade 3/4, untreated uni‐ or bilateral hydrosalpinx, previous endometrial scratching, untreated endocrine abnormalities, intermenstrual blood loss, previous Caesarean section with niche‐formation and intracavitary fluid visible on ultrasound, increased risk of intra‐abdominal infection, oocyte donation cycles or preimplantation genetic testing
Interventions	Study group: single endometrial scratch in the menstrual cycle prior to the start of stimulation for IVF/ICSI. The scratch was performed either in the mid‐luteal phase of a natural cycle or in a cycle with hormonal contraceptives, using an endometrial biopsy catheter Control group: no procedure
Outcomes	Reported in paper: live birth, clinical pregnancy, miscarriage, pain, bleeding Obtained from author correspondence: multiple pregnancy
Notes	Trial registration: NTR 5342 (registered July 2015, registered prospectively) Additional concerns and comments: none Funding: Dutch organisation for funding of healthcare research ZonMW. Author correspondence: yes, undertaken with N.E.vanHoogenhuijze@umcutrecht.nl and H.Torrance@umcutrecht.nl Publication: Full‐text.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Paper states quote: "Participants were randomised 1:1 to the intervention or control group by a centrally‐located, non‐centre‐stratified, web‐based randomisation programme using randomly permuted blocks, with block size varying randomly between two and four."
Allocation concealment (selection bias)	Low risk	Supplementary file provided with the paper described adequate processes for randomisation and allocation concealment quote: "Allocation concealment was ensured by the web‐based randomisation programme, as the persons who registered participants for randomisation could not see how many participants had already been randomised or what their allocation was"
Blinding of participants and personnel (performance bias) All outcomes	High risk	No blinding was used. A higher proportion of women in the endometrial injury arm underwent embryo transfer compared to women in the control arm; however there was no impact on the results after adjusting for this observation
Blinding of outcome assessment (detection bias) All outcomes	High risk	The outcome of pain during the procedure and bleeding were self‐reported by participants who were not blind to their treatment allocation
Incomplete outcome data (attrition bias) All outcomes	Low risk	A total of 7 women in the scratch arm and 13 in the control arm did not have primary outcome data: 5 women in the scratch arm and 8 in the control arm were excluded from the analyses. Of these, 2 in the scratch arm, and 7 in the control arm were excluded for not returning a hard copy of their consent form. The refusal to return the form could have resulted from knowledge of trial allocation and therefore be different across the two arms, however the numbers are relatively low. An additional 2 in the scratch and 5 in the control arm were lost to follow‐up for the primary analyses. However, together these numbers are small and unlikely to impact the primary outcome.
Selective reporting (reporting bias)	Low risk	The trial was registered prospectively and the authors provide a transparent supplementary file of all the changes made since study inception/registration, which are minor. All measured outcomes are reported.
Other bias	Low risk	‐