O-030 The impact of aneuploidy on human peri-implantation development: findings from the extended in vitro culture of 191 human embryos
Authors: Azpiroz F , Torra Massana M , Quintana-Vehí A , Pujol A , Franco Iriarte J M , Lledó B , Millet Teruel G , Aurell R , Pérez de la Blanca E , Fernández C , Urries A , Rodríguez-Aranda A , Chuva De Sousa Lopes S M , Popovic M 
Published: July 2024

Abstract

Study question
How does aneuploidy affect lineage specification and the developmental potential of human embryos cultured up to 12 days post fertilization (D12)?

Summary answer
While distinct types of aberrations carry their own risk of embryonic arrest, prevailing aneuploidies appear to compromise lineage specification beyond the blastocyst stage of development.

What is known already
Chromosomal instability is a hallmark of human preimplantation development, with up to 50% of embryos diagnosed as aneuploid following preimplantation genetic testing (PGT). Aneuploidies are a major cause of implantation failure, pregnancy loss and human congenital defects. Yet despite their clinical relevance, the impact of distinct aberrations on early human development remains poorly understood. Innovative platforms for culturing human embryos up to D12 provide an important opportunity for investigating chromosomal instability. Understanding the effects of specific aneuploidies on human peri-implantation development will be key for advancing human embryo research and improving the interpretation of findings from in vitro embryo models.

Study design, size, duration
A total of 191 PGT blastocysts obtained from 103 patients were included in the study. Blastocysts were selected based on their original diagnosis, including embryos with single whole-chromosome aneuploidies (single trisomies, n = 37 and single monosomies, n = 71), single segmental aberrations (n = 22), embryos with complex chromosomal constitutions (two or more abnormalities, n = 44), as well as control euploid embryos (n = 17).

Participants/materials, setting, methods
Vitrified blastocysts were warmed and cultured up to D12 using an optimized protocol to generate embryo outgrowths. We correlated the original PGT diagnoses to developmental outcomes, including outgrowth viability, morphology and outgrowth size. We evaluated blastocyst quality using the Gardner grading system. Following culture, we immunostained 38 viable outgrowths for lineage-specific markers, including OCT4 (epiblast), GATA6 (hypoblast) and CK-7 (trophoblast). Fisher’s exact test was used for statistical analysis (p &lt; 0.05 was considered significant).

Main results and the role of chance
Following extended culture, 43.5% of embryos remained viable and attached, while 56.5% degenerated and detached. No significant correlation was found between embryo grade and attachment rate. Euploid embryos exhibited the highest attachment rate, with 88.2% (15/17) forming viable outgrowths. Euploid embryos also generated significantly larger outgrowths than trisomic and monosomic embryos (p = 0.01). Embryos diagnosed with trisomies and segmental aberrations exhibited attachment rates comparable to euploid embryos, at 70.3% (p = 0.18) and 68.2% (p = 0.25), respectively. However, embryos with monosomies and complex chromosomal constitutions arrested more readily (28.2% and 15.9% viable, &lt;0.00001, respectively). All euploid embryos (6/6) retained a discernible OCT4+ epiblast-like structure. This was similar to embryos with segmental aberrations and trisomies, with 75% (3/4) and 53.8% (7/13) of outgrowths containing OCT4+ cells, respectively. Nonetheless, distinct trisomies exerted varying effects on peri-implantation development in vitro. For instance, viable trisomies (13, 18, 21) developed similarly to euploid embryos, while outgrowths carrying a trisomy 22 had fewer OCT4+ cells (p = 0.02) and a higher number of GATA6+ cells (p &lt; 0.01), suggesting a potential lineage proliferation defect. Monosomies had the most profound effects on development. Compared to euploid embryos, monosomic embryos formed significantly fewer OCT4+ outgrowths (28.6%, p = 0.02) and contained fewer epiblast (p &lt; 0.0001) and hypoblast-like (p = 0.003) cells.

Limitations, reasons for caution
The limited number of embryos in certain groups warrants careful interpretation. The central drawback of the models is that embryo outgrowths are predominately flattened, which confounds identification of three-dimensional structures formed during normal embryogenesis. Future studies should encompass additional lineage specification markers and potential culture refinements to enhance our interpretation.

Wider implications of the findings
Our findings underscore the critical importance of reporting the chromosomal composition of human embryos utilized for research. This practice will enable a more nuanced interpretation of results from in vitro embryo models and ultimately advance our capabilities in human embryo research.

Trial registration number
not applicable