Hilton 2019.

Study characteristics
Methods	RCT, 2 arms, 51 participants Setting: Canada, three centres Recruitment period: May 2013 to May 2015
Participants	Criteria related to previous IVF failure: yes, first or second IVF cycle Inclusion criteria: with or without ICSI; age 18–39 years; BMI 18–35 kg/m2 ; evaluation of uterine cavity (hysterosalpingogram, sonohysterogram, hysteroscopy) performed in the preceding 24 months; early follicular phase (day 2 or 3) serum FSH evaluated in the preceding 6 months; use of a long gonadotropin‐releasing hormone agonist or antagonist protocol; and documented LH surge 9–11 days before enrolment for patients not pretreated with the oral contraceptive pill or use of the pill for ≥ 10 days at the time of enrolment. Exclusion criteria: previously enrolled in this study; had prior early follicular phase follicle‐stimulating hormone level ≥ 12 IU/L; previous poor ovarian response (defined as prior IVF cycle cancelled for poor response or≤ 4 oocytes retrieved); IVF for preimplantation genetic diagnosis or fertility preservation, diabetes mellitus or uncontrolled thyroid disease; abnormal uterine cavity; untreated hydrosalpinx; any contraindication to endometrial biopsy, or if they had office hysteroscopy or other uterine procedure planned or performed during the cycle preceding IVF stimulation; or planned on using surgically retrieved sperm.
Interventions	Study group: a single endometrial biopsy performed 5‐10 days prior to the start of gonadotropins in a standard IVF cycle Control group: no intervention
Outcomes	Reported in paper: [ive birth, clinical pregnancy, miscarriage Obtained by author correspondence: ‐
Notes	Trial registration: NCT01983423 (registered Nov 2013, registered retrospectively by only 6 months) Additional concerns and comments: none Funding: Unrestricted Educational Grant from Ferring Inc. (Canada) Author correspondence: Undertaken with JHavelock@pacificfertility.ca and Kimberly.Liu@sinaihealthsystem.ca Publication: full‐text.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Authors described quote: "The SAS System for Windows was used generate randomization numbers that were accessed electronically using an encrypted web‐based randomization system"
Allocation concealment (selection bias)	Low risk	As per the above description, allocation was concealed until the point of randomisation
Blinding of participants and personnel (performance bias) All outcomes	High risk	Study described as quote:"open‐label"
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Only objective outcomes reported
Incomplete outcome data (attrition bias) All outcomes	Low risk	Appears to be no attrition, this was confirmed by study authors
Selective reporting (reporting bias)	Low risk	Trial registered six months after initiating recruitment and all listed outcomes reported
Other bias	Low risk	Trial stopped early when only 51/332 intended participants recruited. Recruitment was closed due to difficulty recruiting, which is not itself considered a risk of bias.