P–252 The correlation of first cleavage and blastulation timing to the euploid status of embryos after PGT-A
Authors: Timotheou E , Chartomatsidou T , Kostoglou K , Papa E , Ioakeimidou C , Najdecki R , Papanikolaou E 
Published: August 2021

Abstract

Study question
To examine the correlation of first cleavage and blastulation timing on euploidy rates in IVF cycles after PGT-A.

Summary answer
The timing of blastulation is observed earlier in the euploid embryos.

What is known already
Embryo evaluation is one of the most critical processes that affect the clinical outcome in IVF cycles. Conventional morphologic assessment and morphokinetic assessment using time lapse technology are performed in order to select the embryo with the higher implantation potential to be transferred. It is stated that embryos with faster developmental potential, especially early forming blastocysts, show increased euploidy rate and higher implantation potential.

Study design, size, duration
This study includes ICSI/PGT-A treatments completed between May 2018 and December 2019. 117 blastocysts were biopsied and their euploidy status was analyzed by NGS. These embryos resulted from 32 different ICSI treatments. PGT-A was performed due to: a) repeated IVF failure, b) advanced maternal age, c) recurrent pregnancy loss.ICSI was implemented in all cases and blastocysts were vitrified awaiting the genetic results. Single euploid blastocyst transfer followed and clinical pregnancy rate was monitored.

Participants/materials, setting, methods
Based on the genetic results, the biopsied embryos were divided into two categories; group A representing the euploid embryos and group B the aneuploid embryos. The timing of 1st cleavage and the timing of blastulation, by means of forming a blastocoel, were investigated and compared between the two groups. The rate of early blastocysts in the two groups was also analysed. Early blastocysts are considered those formed at 96h ±2 of embryo culture post ICSI.

Main results and the role of chance
After the genetic analysis of the biopsied embryos, 37 blastocysts were included in group A-Euploid embryos and 80 blastocysts in group B-Aneuploid embryos. The mean time of the 1st cleavage division was similar between the two groups, with marginally no statistical significance (group A-euploid:25.9h, group B-aneuploid: 26.9h ,p&gt;0.05). Regarding the blastulation time, it was achieved earlier in group A-Euploid, at a mean time of 102.6h, compared to the mean time of 106h in group B-Aneuploid (p &lt; 0.05). Between the cohort of the Euploid embryos (group A), there was a higher rate of early blastulating embryos, compared to the cohort of aneuploid embryos (Group B) (24% VS 17.5%), although it was not statistically significant (p &gt; 0.05). After transferring 1 euploid blastocyst, the ongoing pregnancy rate was monitored in 76.5%, independently of the 1stcleavage and blastulation time of the transferred embryo.

Limitations, reasons for caution
Further investigation in larger randomized studies is required, as only a limited number of cases were included in this study. Further analysis of the ongoing pregnancy rate between the euploid blastocysts, depending on other morphokinetic parameters would be of paramount significance, as well.
Wider implications of the findings: High clinical pregnancy rates observed independently of the analyzed time points, indicate high success rates obtained after PGT-A/NGS. Additionally, success rates show that trophectoderm biopsy is not hazardous for the embryo viability, if performed properly. Concluding, genetic testing combined with time-lapse microscopy may provide further information to improve IVF outcomes.

Trial registration number
N/A