Mak 2017.

Study characteristics
Methods	RCT, 2 arms, 229 randomised Setting: Hong‐Kong, research/academic institution, one centre Study period: March 2013 to April 2016 (unclear if recruitment period or whole study period)
Participants	Criteria related to previous IVF failure :no Inclusion criteria: scheduled for frozen embryo transfer (FET) cycles using non‐donor oocytes, normal ovulation and were deemed suitable for natural‐cycle FET Exclusion criteria: any uterine anomaly or pathology such as endometrial polyps, endometriomas larger than 4 cm or hydrosalpinx.
Interventions	Study group: pipelle procedure performed once in the mid‐luteal phase of the cycle preceding the embryo transfer cycleControl group: endocervical manipulation with pipelle, performed once in the mid‐luteal phase of the cycle preceding the embryo transfer cycle
Outcomes	Reported in paper: live birth/ongoing pregnancy, clinical pregnancy, miscarriage, multiple pregnancy Obtained by author correspondence: ‐
Notes	Trial registration: ChiCTRTRC‐12002389 (registered Aug 2012, registered prospectively) Additional concerns and comments: None Funding: None stated Author correspondence: minimal correspondence with jennifermak@cuhk.edu.hk Publication: full‐text.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote:"computer generated random numbers"
Allocation concealment (selection bias)	Unclear risk	The random numbers were quote:"concealed in opaque envelopes" unclear if SNOSE
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Sham procedure used.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Only reporting objective outcomes
Incomplete outcome data (attrition bias) All outcomes	Low risk	8/115 and 5/114 women withdrew from the trial (small numbers)
Selective reporting (reporting bias)	Low risk	Registered prospectively and all outcomes reported
Other bias	Low risk	‐