Aflatoonian 2016.

Study characteristics
Methods	RCT, 2 arms, 100 randomised Setting: Iran, research/clinical centre, one centre Study period: March 2015 to January 2016 (recruitment period unclear)
Participants	Criteria related to previous IVF failure: none Inclusion criteria: women indicated for frozen embryo transfer treatment, had one or more frozen embryo(s) and had a normal uterine cavity (confirmed by vaginal ultrasonography). Exclusion criteria: <40 years (assume error > 40), history of endocrine disorders (hypothyroidism, diabetes mellitus), intrauterine abnormality (uterine polyp, sub‐mucosal fibroma, intrauterine adhesion) and severe endometriosis diagnosed by laparoscopy or endometrioma in ultrasound scanning.
Interventions	Study group: pipelle procedure once between days 21‐23 of the cycle prior to the embryo transfer cycle Control group: no procedure
Outcomes	Reported in paper: ongoing pregnancy, clinical pregnancy, miscarriage, multiple pregnancy Obtained by author correspondence: ‐
Notes	Trial registration: IRCT2015101324512N1 (registered November 2015, retrospective registration) Additional concerns and comments: recruitment rate was high at approximately 14 patients per month. The first author is also the first author of an RCT which has been retracted for methodological issues, which may have been misrepresented (e.g. not a true RCT) (Aflatoonian 2013). The first author has published a large number of trials as first author recently (total of five RCTs as first author in the last 10 years). Additionally, the implantation rates are not consistent with the clinical pregnancy and multiple pregnancy rates; which raises some concern about how the validity of the results. Funding: the financial supporter was Research and Clinical Center for Infertility, Shahid Sadoughi University of Medical Sciences, Yazd, Iran. Author correspondence: Attempted, however no response received Publication: full‐text
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Paper states quote: "a computer‐generated randomization table was created" but also that "93 consecutive subjects" were recruited, therefore unclear whether truly randomised
Allocation concealment (selection bias)	Unclear risk	No description
Blinding of participants and personnel (performance bias) All outcomes	High risk	No blinding employed
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Only reporting objective outcomes
Incomplete outcome data (attrition bias) All outcomes	Low risk	Appears to be no attrition
Selective reporting (reporting bias)	High risk	Retrospective trial registration and not reporting live birth or adverse events such as pain/bleeding
Other bias	High risk	Trial registered retrospectively. Additionally, the implantation rates are not consistent with the clinical pregnancy and multiple pregnancy rates; which raises some concern about how the validity of the results.