| dc.description.abstract | Mosaicism, a condition characterized by the coexistence of chromosomally normal (euploid)
and abnormal (aneuploid) cells within an embryo, poses significant challenges in assisted
reproductive technologies (ART), including in vitro fertilization (IVF). Euploid cells have the
appropriate number of chromosomes, essential for healthy development, whereas aneuploid
cells, with either too many or too few chromosomes, can impair embryo viability, increase
miscarriage risk, and reduce IVF success rates. This review provides an overview of
mosaicism types, errors causing the aneuploidy, and implications for embryonic viability and
pregnancy outcomes.
The severity of mosaicism mostly depends on the proportion of aneuploid cells. Low-level
mosaicism, involving a smaller fraction of abnormal cells, has a lesser impact on
development and pregnancy outcomes, while high-level mosaicism can compromise embryo
survival. Additionally, the nature of the chromosomal abnormalities, such as whole
chromosome gains or losses, further influences developmental potential.
Chromosomal instabilities may originate either during meiosis, the process of gamete
formation, or during post-fertilization mitotic divisions. Meiotic errors, often associated with
advanced maternal age, result in uniform aneuploidy across all embryonic cells and do not
contribute to mosaicism. Conversely, mitotic errors, including anaphase lagging, spindle
checkpoint failures or slow/stalled replication fork, occur during early embryonic divisions and
are the primary source of mosaicism. These errors cause the initial identical cells to acquire
different chromosomal compositions as the embryo divides, leading to a mosaic state.
Pre-implantation Genetic Testing for Aneuploidy (PGT-A) is a valuable tool for identifying
chromosomal abnormalities in embryos prior to transfer. PGT-A is not universally
implemented, and variability in testing methodologies across clinics may lead to inconsistent
outcomes, including the unnecessary discarding of potentially viable embryos.
To address these concerns, this review states the importance for standardization in testing
protocols and embryo assessment criteria. It proposes a hierarchical approach to embryo
selection, prioritizing euploid embryos, followed by low level mosaic embryos, and reserving
high level mosaic embryos as a last option. Finally, this review discusses the future of
embryo selection, emphasizing advancements such as non-invasive genetic testing and
artificial intelligence-driven assessment tools. These technologies could improve success
rates, minimize ethical dilemmas surrounding embryo disposition, and enhance the safety
and effectiveness of reproductive treatments | |
