Segmental aneuploidy in human blastocysts: a qualitative and quantitative overview

Area of Science:

• Reproductive biology
• Genetics
• Embryology

Background:

• Segmental aneuploidy is common in human oocytes and embryos.
• Limited research exists on the characteristics of chromosomal segments in developing embryos.

Purpose of the Study:

• To analyze the incidence, type, size, and chromosomal distribution of segmental aneuploidies in blastocysts.
• To investigate factors influencing segmental aneuploidy, such as trophectoderm quality and clinical indications.

Main Methods:

• Retrospective analysis of 3565 blastocysts undergoing preimplantation genetic testing for aneuploidies (PGT-A).
• Next-generation sequencing (NGS) used for trophectoderm sample analysis.
• Segmental aneuploidies defined as fragments >5 Mb; pure single segmental aneuploidies (SSA) were statistically analyzed.

Main Results:

• 8.4% of blastocysts showed segmental aneuploidy; 4.5% had pure SSA.
• SSA was more frequent in medium-sized chromosomes, particularly q-arms, and correlated with trophectoderm quality.
• SSA size related to chromosome number and arm, with larger chromosomes having larger absolute SSA sizes, but a constant ratio (<50% of chromosome).

Conclusions:

• SSA frequency is chromosome- and topography-dependent, influenced by trophectoderm quality.
• SSA incidence is not linked to clinical or embryological factors.
• Potential origins of SSA include chromosome instability, chromothripsis, biopsy bias, or iatrogenic effects.