Vuong 2018.

Study characteristics
Methods	Single‐centre RCT, My Duc Hospital, Ho Chi Minh City Conducted: Vietnam Enrolment: June 2015‐April 2016 Power calculation: stated Randomisation: performed by an independent study co‐ordinator by means of block randomisation using a computer‐generated random list Timing of randomisation: on day 3 after retrieval Nature of intervention: Cryotech vitrification method Follow‐up: cumulative ongoing pregnancy rate and LBR (including all FETs performed within the 12 months after the initial transfer)
Participants	782 women (391 freeze‐all, 391 control) Inclusion criteria: First or second IVF cycle Possibility to undergo ET on day 3 At least 1 grade 1 embryo on day 3 available Agreement that a maximum of 2 embryos would be transferred Exlusion criteria: history of PCOS (based on the Rotterdam criteria), in vitro maturation with polycystic ovaries visible on the ultrasonography or cycle with oocyte donation.
Interventions	For women who were assigned to the fresh‐embryo group, a maximum of 2 grade 1 or 2 embryos were transferred on day 3. Any remaining grade 1 or 2 embryos, along with grade 3 embryos (if requested by the couple), were frozen and transferred in subsequent cycles if needed. In the FET group, there was no fresh transfer and all grade 1 and 2 embryos had been cryopreserved on day 3 by means of the Cryotech vitrification method. In menstrual cycles following the ovum pick‐up the endometrium was artificially prepared for transfer using estradiol and progesterone for transfer of a maximum of 2 embryos.
Outcomes	The primary outcome was ongoing pregnancy after the first ET. Prespecified secondary outcomes were the rates of implantation, clinical pregnancy, ectopic pregnancy, miscarriage, live birth, multiple pregnancy, vanishing‐twin pregnancy, and OHSS. Pregnancy complications for pregnancies that continued beyond 24 weeks, complications were recorded. Time to pregnancy was calculated in a post hoc analysis at 12 months after randomisation using the median to pregnancy.
Notes	Funding: by My Duc Hospital
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Performed by an independent study co‐ordinator by means of block randomisation using a computer‐generated random list
Allocation concealment (selection bias)	Unclear risk	Randomised women by means of block randomisation by an independent study co‐ordinator using a computer‐generated random list, there was no further explanation about allocation concealment.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Blinding of doctors and participants was not possible due to the nature of the intervention.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Outcome assessor blinding was not reported, however primary outcome is not likely to be influenced by lack of blinding.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Data were analysed for all randomised women.
Selective reporting (reporting bias)	Low risk	All registered outcomes were reported. Protocol publication. Study was registered in a prospective trial register with the trial number: NCT02471573.
Other bias	Unclear risk	Not reported on blinding of doctors to interim analyses of outcomes of the study. Blinding of investigators was not reported (which is relevant for determining end of study).