P-261 Embryo compaction based on time-lapse imaging is a valuable parameter for selecting blastocysts with the highest developmental potency and associated with a ploidy state
Authors: Jeon Y , Lee S Y , Bang S , Park J K , Eum J H , Kim J W , Kwak I P , Lee W S 
Published: June 2023

Abstract

Study question
Does embryo compaction positively correlate with blastocyst development and further embryonic ploidy status?

Summary answer
Fully compacted embryos develop into good-quality blastocysts, have shorter developmental times, and are related to ploidy status.

What is known already
To succeed in assisted reproduction technique (ART), it is necessary to select embryos that have the highest potential. So, numerous studies make an effort to establish parameters for selecting embryos. A Time-lapse system (TLS) allows embryologists to understand dynamic embryo change through continuous monitoring. In development, embryos undergo dynamic functional changes during compaction, which play a crucial role in blastocyst formation. It is also known that embryonic genome activation can be seen with compaction. Incomplete compaction leads to blastocyst developmental failure. Nevertheless, the details about the compaction of human embryos have not been paid sufficient attention, so still rarely known.

Study design, size, duration
This was a retrospective cohort study including couples that underwent an IVF cycle at the CHA Fertility Center, Gangnam, between January 2019 to October 2022. A total of 371 reached the blastocyst from 113 patients cultured in the TLS were analyzed. Among these, 94 blastocysts were analyzed by preimplantation genetic testing for aneuploidy (PGT-A). Statistical analysis was performed by prism9 using a t-test and chi-square test. P values &lt;0.05 were regarded as statistically significant.

Participants/materials, setting, methods
Embryos were classified into two categories by compaction pattern: fully compacted (Group1, N = 194) and partially compacted (Group2, N = 177). Blastocyst quality was determined by morphology and divided into three groups (Good, Average, and Poor). The developmental time ranging from morula to blastocyst was annotated based on the embryo scope image. The surface of the blastocyst was measured every hour starting at blastocyst formation (tB) by using the ellipse tool of the Embryo Viewer software.

Main results and the role of chance
Good and average quality blastocysts are significantly higher in Group 1 than in Group 2 (21.6% vs. 3.4%, p &lt; 0.01; 47.9% vs. 26.6%, p &lt; 0.01, respectively). In contrast, poor-quality blastocysts are lower in Group 1 than in Group 2 (30.4% vs. 70.1%, p &lt; 0.01). The beginning and completion of compaction, and blastocyst formation times of embryos from Group 1 were significantly shorter than those of embryos that Group 2(78.6h vs. 82.4, p &lt; 0.01; 87.0h vs. 92.2h, p &lt; 0.01; 100.2h vs. 103.7, p &lt; 0.01, respectively). Also, there is a significant difference in longitudinal surface area at 3, 6, and 12h from the time of tB between the two groups. Consequently, the average expansion rate in Group 1 was significantly faster than in Group 2 (653.6 μm2/hour vs. 499.2μm2/hour, p &lt; 0.05). According to the result of PGT-A, Group 1 had statistically significantly higher euploid and lower aneuploidy rates compared to Group 2 (47.2% vs. 36.2%, p &lt; 0.001; 52.8% vs. 63.8%, p &lt; 0.001, respectively). However, in the PGT-A group, there was no significant difference in developmental time between the two groups, regardless of fully or partial compaction. Meanwhile, the average expansion rate in euploidy blastocyst was significantly faster than in aneuploidy blastocyst (747.8 μm2/hour vs. 564.3 μm2/hour, p &lt; 0.05).

Limitations, reasons for caution
The main limitation is the single-center retrospective approach. Therefore future prospective research is needed to verify and extend our findings. Another one, in the PGT-A there was no difference in developmental time regardless of fully or partially compaction. The reason is that we selected blastocysts of sufficient quality for biopsy.

Wider implications of the findings
Using the TLS, we have observed the dynamics of compaction in detail. We found a positive relationship between compaction and blastocyst quality and its association with embryo ploidy. The assessment of compaction is a significant parameter for predicting competent embryos and should be given priority when selecting blastocysts.

Trial registration number
Not applicable