Human embryo mosaicism: did we drop the ball on chromosomal testing?

Area of Science:

• Reproductive Medicine
• Genetics
• Embryology

Background:

• Chromosomal mosaicism is more prevalent in in vitro fertilization (IVF) embryos compared to prenatal samples.
• Trophectoderm (TE) biopsy for pre-implantation genetic screening (PGS) can lead to diagnostic errors due to mosaicism.
• Current diagnostic techniques have limitations in detecting mosaicism in TE biopsies.

Purpose of the Study:

• To highlight the challenges posed by mosaicism in PGS for IVF embryos.
• To discuss the implications of mosaicism on diagnostic accuracy and embryo transfer decisions.
• To emphasize the need for informed consent regarding mosaicism detection limitations.

Main Methods:

• Review of existing literature on chromosomal mosaicism in IVF embryos and PGS.
• Analysis of diagnostic limitations of TE biopsy and current genetic assessment methodologies.
• Clinical implications of mosaicism on embryo viability and implantation potential.

Main Results:

• PGS may misdiagnose aneuploid embryos as euploid or vice versa due to mosaicism.
• The accuracy of mosaicism detection is limited by biopsy size, cell location, and assessment methods.
• Clinical outcomes are influenced by the specific chromosomes affected and the developmental timing of mosaicism.

Conclusions:

• Consideration of transferring chromosomally abnormal embryos with non-viable aneuploidies is warranted when no euploid options exist.
• Informed consent must acknowledge the potential impact of undetected mosaicism on PGS results.
• The understanding and management of mosaicism represent a significant shift in current IVF practices.