1. Live birth rate after first transfer.

Outcome	Number of studies	Number of participants	Analysis method	OR
Live birth ratea after first embryo transfer for all embryo stages of transfer	13	7766	Odds ratio (Mantel‐Haenszel, fixed‐effect, 95% confidence interval)	1.17 (95% CI 1.06 to 1.28)

^aLive birth rate calculated after first transfer is added for illustrative purposes as this comparison is often reported in the literature. It possibly shows differences in outcome for a stimulated and an unstimulated uterus, although this does not take into account the number of embryos that were thawed for transfer. This outcome is less relevant for women undergoing treatment since at the same time of first transfer in a freeze‐all strategy, they would already have received the second transfer (as long as there was a sufficient number of embryos) in a conventional strategy that includes fresh transfer. Here, one could consider the result of the first embryo transfer in the frozen group against the combined outcomes of the fresh transfer and the first frozen‐thawed‐transfer in the fresh group. Therefore cumulative live birth rate is the relevant outcome for women.

For the calculated live birth rate after the first embryo transfer, we included the eight studies included for the primary outcome (Chen 2016; Ferraretti 1999; Santos‐Ribeiro 2020; Shapiro 2011a; Shapiro 2011b; Vuong 2018; Wei 2019; Wong 2021) and five additional RCTs: Aflatoonian 2018; Aghahosseini 2017; Coates 2017; Shi 2018; Stormlund 2020. We contacted the authors for additional information regarding cumulative data by email but we did not receive a response.

Aflatoonian 2018 compared live birth rate after the first embryo transfer between a freeze‐all strategy and a conventional strategy in high responders at risk for developing OHSS. Aghahosseini 2017 included infertile women who were candidates for an in vitro fertilisation (IVF) treatment with no further specification of age or type of responder. Coates 2017 excluded women with a suspected decreased ovarian reserve (based on serum follicle‐stimulating hormone and anti‐Müllerian hormone. Women in both groups underwent IVF with assisted hatching and pre‐implantation genetic screening. Shi 2018 compared live birth rate after the first embryo transfer between a freeze‐all strategy and a conventional strategy in young women with a regular menses and the reason for IVF procedure: tubal factor, male factor, or both. Stormlund 2020 compared live birth rate after the first embryo transfer between a freeze‐all strategy and a conventional strategy in young women with a regular menses and the reason for IVF procedure: male, tubal, uterine, or unexplained infertility.