Mackens 2020.

Study characteristics
Methods	RCT, 2 arms, 200 randomised Setting: Belgium, one University Hospital. Recruitment period: April 2014 ‐ October 2017 (confirmed with authors)
Participants	Criteria related to previous IVF failure: no Inclusion criteria: 18‐40 years of age; fresh IVF/ICSI cycle; antagonist downregulation; signed informed consent Exclusion criteria: other known reasons for impaired implantation (i.e. hydrosalpinx, fibroid distorting the endometrial cavity, Asherman’s syndrome, thrombophilia or endometrial tuberculosis); oocyte donation acceptors; frozen egg transfers; embryos planned to undergo embryo biopsy; BMI >35 or <18; women already recruited for another trial on medically assisted procreation during the same cycle; women who have previously enrolled in the trial; those unable to comprehend the investigational nature of the proposed study
Interventions	Study group: endometrial biopsy was performed on Days 6 to 8 of ovarian stimulation with a Pipelle de Cornier® (Laboratoire CCD, France). The device was introduced into the uterus until slight resistance from the fundus was felt after which the piston was withdrawn and the device rotated through 360◦ as it was moved up and down for four times Control group: no intervention
Outcomes	Reported in paper: live birth, clinical pregnancy, miscarriage, bleeding, pain Obtained by author correspondence: ‐
Notes	Trial registration: NCT02061228 (registered Feb 2014, registered prospectively) Additional concerns and comments: the trial authors conduct a large number of RCTs run at this single academic centre. However, all RCTs were found to be staggered and conducted in non‐overlapping populations. Funding: ‘Fonds Wetenschappelijk Onderzoek’ (FWO, Flanders, Belgium, 11M9415N, 1524417N). Author correspondence: yes, with Shari Mackens Shari.Mackens@uzbrussel.be and Samuel dos Santos Ribeiro, samueldsribeiro@gmail.com Publication: full‐text.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	As per paper quote: "randomization sequence and allocation was appointed using a computer‐generated randomization list with a 1:1 allocation”
Allocation concealment (selection bias)	Low risk	Quote:“concealment was ensured with sequentially numbered, opaque, sealed envelopes”
Blinding of participants and personnel (performance bias) All outcomes	High risk	No blinding
Blinding of outcome assessment (detection bias) All outcomes	High risk	No blinding and subjective outcomes reported: pain and bleeding
Incomplete outcome data (attrition bias) All outcomes	Low risk	Only 1 women withdrew in the control group
Selective reporting (reporting bias)	Low risk	Trial was registered prospectively and reports all review outcomes originally planned. Some additional outcomes such as premature birth and low birth weight not reported, but not review outcomes
Other bias	High risk	The quote:"trial was terminated prematurely following the second interim analysis after the recruitment of 200 patients due to safety concerns (specifically, a potentially increased risk of miscarriage in the intervention arm)" and there does not appear to be any statistical adjustment made for these multiple interim analyses