P-722 Impact of blastocyst quality and post-thaw embryo culture factors in non-invasive PGT-A informativity on vitrified blastocysts.
Authors: Garcia Pascual C M , Ardestani G , Banti M , Navarro-Sánchez L , Van Zyl E , Castellón J A , Sakkas D , Simón C , Rubio C 
Published: June 2023

Abstract

Study question
What are the most important factor/s involved in the informativity of non-invasive PGT-A (niPGT-A) of vitrified blastocysts?

Summary answer
The day of vitrification and post-thaw time in culture of vitrified blastocysts are the most important factors for niPGT-A informativity, without correlation with blastocyst quality.

What is known already
niPGT-A is a technique that allows the non-invasive study of the chromosomal content of blastocysts. The informativity and concordance rates for fresh (Rubio, 2020) and frozen-thawed embryos (Garcia-Pascual, 2022) have been related with the time in culture and the day of media collection. However, there is a need to understand the optimal conditions needed to obtain optimal informativity for frozen-thawed vitrified blastocyst undergoing niPGT-A.

Study design, size, duration
Prospective study including 135 spent blastocyst media (SBM) and the corresponding blastocyst samples from thawed day-5 and day-6 blastocysts from PGT-A (73) and niPGT-A (62) cycles collected from January 2021 until March 2022. Blastocysts were discarded under IRB approval. The embryos were divided into 3 groups depending on the day of development and the time in culture after thawing: group-1, day-5 blastocysts cultured 8h; group-2, day-5 blastocysts cultured 24h and group-3, day-6 blastocysts cultured 8h.

Participants/materials, setting, methods
Media and blastocysts were obtained from IVF patients (29-42 years-old). After thawing, each blastocyst was washed to remove remaining cumulus cells and individually transferred to a 10 μL droplet of fresh media or to an EmbryoScope dish with 20 μL per well. SBM and blastocysts were collected, frozen and analysed by Next Generation Sequencing. Correlation between concordance rates (overall agreement between SBM and blastocyst samples), informativity, embryo quality and time in culture were evaluated.

Main results and the role of chance
All the embryos had a good embryo quality (BB or greater using Gardner Criteria) but different expansion degree. Informativity was significantly lower when day-5 embryos were cultured for only 8 hours (group 1), regardless of the degree of expansion (expansion degree 3, 28.57%; degree 4, 64.29% and degree 5-6, 57.14%, p &lt; 0.0005). The concordance rates between SBM and whole blastocysts were very high and no significant different in relation to the expansion degree when comparing day-5 embryos cultured for 8 hours (group 1, 90.5%) with 24 hours (group 2, 93.6%) or with day-6 embryos cultured for 8 hours (group 3, 92.3%). The data suggest that the important factor impacting the informativity rate is the day of vitrification, and the time in culture after thawing, but not the expansion degree of the embryos. Regarding the concordance rates, there is no impact of the time in culture nor the expansion degree.

Limitations, reasons for caution
The main limitation of this study is that all the embryos analysed had fair or good quality but different expansion degrees.

Wider implications of the findings
The high concordance rates observed in frozen blastocysts opens the possibility of expanding the use of niPGT-A to frozen blastocyst without an impact of the expansion degree in the results.

Trial registration number
Not applicable