Pregnancy outcomes after day 5 versus day 6 blastocyst‐stage embryo transfer: A systematic review and meta‐analysis. Issue 4 (5th February 2020) - Li, Yi‐xin
Abstract: Aim: To compare the pregnancy outcomes after day 5 blastocyst‐stage embryo transfers (BET) versus day 6 BET following vitrified‐warmed cycle and to evaluate whether the number of embryos transferred and the chromosomal status of embryo influence effect estimates. Methods: A literature search (PubMed, Embase and MEDLINE) up to January 2019 was conducted to identify studies where women with day 6 BET were compared to women with day 5 BET. Only studies published in English language, on peer‐reviewed journal were considered eligible. The following subgroup analyses were performed: (i) number of embryos transferred and (ii) chromosomal status of embryo. Results: From a total of 1956 articles identified, 23 observational studies were included in the meta‐analysis. We observed that day 6 BET were associated with lower implantation rate (risk ratio, RR: 1.17, 95% confidence interval, CI: 1.10–1.24), clinical pregnancy rate (RR: 1.17, 95% CI: 1.10–1.24), ongoing pregnancy rate (RR: 1.15, 95% CI: 1.07–1.24) and live birth rate (RR: 1.22, 95% CI: 1.11–1.33) than day 5 BET following vitrified‐warmed cycle. The subgroup analysis found that the superiority of day 5 BET compared with day 6 BET is influenced by the number of embryos transferred and chromosomal status of embryos. Conclusion: Current evidence shows that day 5 BET is superior to day 6 BET following vitrified‐warmed cycle in clinical practice. Due to the overall low quality of available evidence, more larger and well‐conducted studies are needed to compare the pregnancy outcomes between day 5 and day 6 BET before drawing a clear conclusion.