Single blastocyst stage versus single cleavage stage embryo transfer following fresh transfer: A systematic review and meta-analysis

To compare the available evidence of the effectiveness of single blastocyst stage transfer against the effectiveness of single cleavage stage embryo transfer.A systematic research based on Pubmed, Embase and the Cochrane Library was performed until May 2, 2020 to identify all relevant studies. The Cochrane Collaboration's Review Manager (RevMan) 5.0.2 software was used for statistical analysis.Five randomized controlled trials (RCTs) were included in analysis, involving 1784 patients in total, who were divided into 2 groups, which were the single blastocyst stage transfer (SBT) group of 932, and the single cleavage stage transfer (SCT) group of 852. Our meta-analysis concluded that SBT group had a significantly higher clinical pregnancy rate (RR 1.26; 95%CI: 1.14-1.39), ongoing pregnancy rate (RR 1.19; 95%CI: 1.05-1.35) and delivery rate (RR 1.4; 95%CI: 1.13-1.75) than SCT group during the fresh transfer. While miscarriage rate (RR 0.93; 95% CI: 0.66-1.33), multiple pregnancy rate (RR, 1.12; 95% CI, 0.51-2.45) and ectopic pregnancy rate (RR, 0.5; 95% CI: 0.13-1.90) between two groups showed no significant difference. However, the SCT group contained notably more cryopreserved embryos than the SBT group. (RR -0.68, 95% CI: -0.95 to -0.41).Our results indicate that single blastocyst stage transfer is associated with higher ongoing pregnancy rate and delivery rate comparing to single cleavage stage transfer in the clinical practice. Due to the low quality of the evidence of the primary outcomes, other higher-quality lager RCTs are necessary before a fully informed decision is made.