Shi 2018.

Study characteristics
Methods	Multicenter RCT Conducted: 20 reproductive medical centres throughout China Enrolment: March 2015‐March 2017 Power calculation: stated Randomisation: by means of an online central randomisation system (www.medresman.org) Timing of randomisation: on the day of oocyte retrieval Nature of intervention: day 2 or 3 embryo cryopreservation by means of vitrification Follow‐up: LBR after the first ET
Participants	2157 women (1077 freeze‐all, 1080 control) Inclusion criteria: Women who underwent their first cycle of IVF with or without ICSI Women with regular menses (defined as a spontaneous cycle length of ≥ 21 days and ≤ 35 days) Reason for IVF procedure: tubal factor, male factor, or both Age between 20 and 35 years Duration of infertility of > 1 year Exclusion criteria: women with a history of unilateral oophorectomy, recurrent spontaneous abortion, diagnosis of the PCOS, or uterine abnormality (e.g. Müllerian duct anomaly, adenomyosis, submucous myoma, intra‐uterine adhesion, or scarred uterus) were excluded. Women were also excluded if they had a chronic medical condition that has been associated with adverse pregnancy outcomes, such as hypertension, symptomatic heart disease, diabetes mellitus, liver disease or dysfunction (according to the results of serum liver‐enzyme testing), renal disease or abnormal renal function, severe anaemia, history of deep venous thrombosis, pulmonary embolus, or cerebrovascular accident. All the couples were screened with the use of karyotyping, and those with an abnormal karyotype were excluded.
Interventions	In women who were assigned to the fresh embryo group, luteal‐phase support with was started immediately after oocyte retrieval and was continued until the day of serum hCG testing. On day 2 or 3 of the embryo culture, up to 2 embryos were selected and transferred. In women who were assigned to the FET group, all the embryos were vitrified. 2 good‐quality embryos were vitrified on day 2 or day 3, and the other embryos could be vitrified at the cleavage or blastocyst stage. At the second spontaneous menstrual cycle after oocyte retrieval, natural ovulation was monitored by means of ultrasonography. Luteal‐phase support was started from the day of ovulation. Up to 2 day 2 or day 3 frozen embryos were thawed and transferred 2 or 3 days after ovulation. If the natural ovulation cycle was cancelled owing to anovulation or poor endometrial development, an artificial cycle was used for endometrial preparation in the next menstrual cycle.
Outcomes	The primary outcome was: a live birth after the first ET. Prespecified secondary efficacy outcomes included biochemical pregnancy, implantation, clinical pregnancy, ongoing pregnancy, pregnancy loss, and birth weight. Safety outcomes included moderate or severe OHSS, ectopic pregnancy, congenital anomaly, and obstetric and perinatal complications (i.e. gestational diabetes, gestational hypertension, pre‐eclampsia, placenta praevia, placental abruption, preterm delivery, neonatal hospitalisation for > 3 days, and perinatal death).
Notes	Funded by the National Key Research and Development Program of China and the National Natural Science Foundation of China. We requested additional information regarding cumulative data from the authors by email but we did not receive a response.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	By means of an online central randomisation system (www.medresman.org).
Allocation concealment (selection bias)	Low risk	By means of an online central randomisation system (www.medresman.org). The randomisation sequence was generated and kept by the data‐coordinating centre and was not accessible to the investigators who enrolled women.
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 trials register with the trial number: ChiCTR‐IOR‐14005406.
Other bias	Unclear risk	(Cumulative) data per subsequent menstrual or cryo‐transfer cycle not reported (relevant for time‐to‐pregnancy comparison and the related comparison of results after first transfer in FET group vs results after first 2 transfers in fresh group).