The Impact of Embryo Quality on Pregnancy Outcomes in Single Day 5 versus Day 6 Euploid Blastocyst Transfer: A Retrospective Cohort Study

Abstract

Background: Selecting embryos with the highest implantation potential is crucial for in vitro fertilization (IVF) success.Both the timing of blastulation, day 5 (D5) or D6, and the embryo quality have been suggested as influentialfactors in determining the clinical outcome of single euploid blastocyst transfers. However, evidence supporting thesuperiority of D5 over D6 blastocysts remains inconclusive. The aim of this study was to compare clinical outcomesfollowing the transfer of euploid blastocysts with different quality and timing of blastulation.Materials and Methods: A retrospective cohort study was conducted at our Assisted Reproductive Center, analyzingthe outcome of 774 transfers with D5 euploids and 155 transfers with D6 euploids performed between January 2019and February 2022.Results: The live birth rate was significantly lower in the euploid D6 group compared to the euploid D5 group (38.71vs.55.04%, P=0.001). The outcome was significantly influenced by the quality of the embryos. Live birth rates were 62.14and 53.61% following transfers of D5 and D6 excellent embryos respectively, 45.18 and 32.21% following transfer ofD5 and D6 good embryos but only 28.64 and 19.32% following transfer of D5 and D6 fair embryos. The outcome differencewas statistically significant across embryo quality categories (P=0.001). The adjusted risk ratios (RR) of clinicaloutcomes indicated that excellent euploid D5 embryos consistently outperformed other types of embryo quality.Conclusion: The timing of blastulation and embryo quality are crucial factors in determining the success of singleeuploid blastocyst transfers. Excellent euploid D5 transfers yielded superior clinical outcomes, providing valuableinsights for IVF teams and patients when selecting embryos to be transferred.

Keywords

• blastocyst transfer
• blastulation timing
• live birth rate