P-515 The morphokinetic signature of high-level mosaic embryos in time-lapse ART analysis
Authors: Yoon S , Jeong J , Kim T  H , Eum J  H , Han J , Kim H , Lee H  J , Han E  J , Park J  E , Kim S  J , Lee W  S 
Published: July 2024

Abstract

Study question
Do high-level mosaic embryos exhibit differences in developmental speed compared to euploid or low-level mosaic embryos?

Summary answer
High-level mosaic embryos exhibit slower development than euploid and low-level mosaic embryos during the blastulation and blastocyst formation stages.

What is known already
Time-lapse technology (TLT) has facilitated the real-time observation of human embryo development without disrupting culture conditions, generating a wealth of morphokinetic data linked to outcomes such as implantation potential, blastocyst development, and ploidy status. However, the developmental patterns of mosaic embryos based on their aneuploidy level using TLT remain not well understood. Consequently, we aimed to assess the clinical significance of morphokinetic parameters in human embryo development, with a specific focus on embryos categorized by their mosaic status.

Study design, size, duration
This retrospective study examined 385 blastocysts undergoing preimplantation genetic testing for aneuploidy (PGT-A) between January and December 2022. Out of the total, 191 expansion blastocysts underwent PGT-A biopsy on day 5. The PGT-A results, which categorized embryos into euploid, aneuploid, and mosaic based on their genetic composition, were determined through next-generation sequencing (NGS) by an analysis company. Mosaic embryos were further categorized into two groups: high-level mosaicism (&gt;30% aneuploidy cells) and low-level mosaicism (≤30%).

Participants/materials, setting, methods
Differences in development rates were assessed through the examination of morphological and morphokinetic parameters. These parameters included the time to second polar body extrusion (tPB2), time to pronuclei appearance and fading (tPNa, tPNf), time to reach 2–8 cells (t2, t3, t4, t5, t6, t7, t8, t9), and time to the onset of blastulation and blastocyst formation (tSB, tB). Statistical analyses, incorporating ANOVA and post-hoc tests, were employed to compare developmental timings across different groups.

Main results and the role of chance
When categorizing mosaic embryos based on their level, high-level mosaic embryos showed a significantly slower developmental rate than low-level mosaic embryos, evident at both the blastulation stage (tsB, high-level vs. low-level: 101.80h vs. 97.3h, p=0.003) and blastocyst stage (tB, high-level vs. low-level: 109.98h vs. 105.92h, p=0.005). In comparison to euploid embryos, low-level mosaic embryos demonstrated comparable outcomes. Conversely, high-level embryos exhibited a significant difference in both blastulation (tsB, euploidy vs. high-level: 98.85h vs. 101.80h, p=0.026) and blastocyst (tB, euploidy vs. high-level: 106.73h vs. 109.98h, p=0.011) stages. These findings suggested that the mosaic level of embryos might influence developmental kinetics, proposing this approach as an additional tool for the selection of mosaic embryos in the context of embryo transfer.

Limitations, reasons for caution
This study focused on morphokinetic parameters captured using time-lapse imaging, which may not fully represent the complex cellular dynamics within embryos. Furthermore, the categorization of mosaic embryos into high-level and low-level groups based on the percentage of mosaicism (&gt;30% and ≤30%, respectively) might not capture all embryo developmental potential.

Wider implications of the findings
The findings suggest valuable predictive potential in assessing the development of aneuploid and mosaic embryos. Further research into the development of euploid, aneuploid, and mosaic embryos, as well as high-level and low-level mosaic embryos, could provide valuable insights for ART practices. This could significantly impact ART decision-making and patient outcomes.

Trial registration number
not applicable