P-249 Morphokinetic parameters comparison between balanced and unbalanced embryos from patients with structural chromosome abnormalities
Authors: Aparicio González M , Herrero Grassa L , Cascales Romero L , Boyano Rodriguez B , Bravo Martin R , Garcia Roa A , Arias Jimenez L  G , Ortiz Salcedo J  A , Ten Morro J , Bernabeu Garcia A , Bernabeu Perez R 
Published: July 2024

Abstract

Study question
Are there morphokinetic differences between balanced and unbalanced embryos after PGT-SR?

Summary answer
The total time embryos remain at the morula stage (TiCAV- TM) could be a morphokinetic marker to consider in PGT-SR cycles.

What is known already
Due to the preimplantation genetic testing for structural rearrangements (PGT-SR) it is possible to identify embryos with an excess or defect of genetic material associated with a parental structural rearrangement. This technique is suitable for patients with a normal phenotype but a balanced chromosomal rearrangement. These patients have a higher risk of spontaneous abortion, as well as higher aneuploidy rates. Within structural chromosomal alterations, translocations are the most common presentation of chromosomal rearrangement.

Study design, size, duration
Within this multicentre retrospective study, we evaluated 133 embryos, from 39 cycles in which one of the partners had a karyotype with balanced reciprocal or Robertsonian translocations, from January 2021 to September 2023. After PGT-SR was carried out, we obtained 40 balanced embryos and 93 unbalanced embryos.

Participants/materials, setting, methods
We compared the conventional morphokinetic parameters and the duration of each state between two groups after PGT-SR samples were analysed. All embryos were cultured in Geri® time-lapse incubators, and underwent embryo biopsy on day 5-7. Statistical analysis was conducted using R software (v.4.3.1), including the following confounding variables: origin of karyotype alteration (maternal or paternal), type of translocation (Robertsonian or reciprocal), female and male gamete age, type of oocyte (fresh or frozen) and oocyte origin.

Main results and the role of chance
We observed that the mean age of the oocyte was significantly higher in the unbalanced embryos compared to the balanced ones (32.85±5.32 years vs.30.45±5.01 years). In terms of the altered karyotype, the paternal origin is more prevalent than the maternal one (60.9% vs. 39.1%). Regarding the type of translocation, reciprocal translocation is more predominant than Robertsonian translocation (83.5% vs. 16.5%) in our study population. When comparing morphokinetic parameters between both groups, we observed that unbalanced embryos tend to reach an expanded blastocyst stage later than balanced embryos (107.62±10.02h vs. 102.48±8.87h, respectively; p = 0.008, corrected p-value=0.186). We observed the same tendency with hatching initiation time (110.64±10.49h vs. 105.91±9.38h; p = 0.013, corrected p-value=0.296). We observed that unbalanced embryos have a slower development than balanced embryos (TiCAV-TFB 10.10±4.46h vs. 8.35±3.79h; p = 0.006, corrected p-value=0.437; TiH-TiCAV 13.03±5.98h vs. 11.79±5.50h; p = 0.017, corrected p-value=0.816). We did observe significant differences in total time at morula stage (TiCAV – TM) when comparing unbalanced and balanced embryos (12.60±6.94 vs. 8.88±5.65; p = 0.003, corrected p-value=0.001).

Limitations, reasons for caution
A higher number of embryos should be evaluated in order to enhance the statistical power of this study, as there is an important difference in sample size between balanced and unbalanced embryos in the PGT-SR cycles included in this study.

Wider implications of the findings
Further morphokinetic study of embryos from patients with structural chromosomal abnormalities can open up new lines of research and can help us to predict the final outcome of the cycle, accompanied by a genetic study.

Trial registration number
Not applicable