Assessing the necessity of screening ≤5 Mb segmental aneuploidy in routine PGT for aneuploidies.

Research Question: Does routine clinical practice require an increase in the resolution of preimplantation genetic testing for aneuploidies (PGT-A) to detect segmental aneuploidies ≤5 Mb?

Design: This retrospective study analysed 963 trophectoderm biopsies from 346 couples undergoing PGT between 2019 and 2023. Segmental aneuploidies ≥1 Mb were reported. The characteristics, clinical interpretation and concordance of segmental aneuploidies ≤5 Mb were analysed.

Results: The incidence of segmental aneuploidies was 15.1% (145/963) in blastocysts, with segmental aneuploidies of ≤5 Mb accounting for 2.3% (22/963). The size of the segmental aneuploidies showed a skewed distribution. Segmental aneuploidies ≤5 Mb were found to occur more frequently on the q arm of the chromosome, compared with the p arm. Losses of ≤5 Mb segmental aneuploidies were more prevalent than gains, with 17 deletions compared with 5 duplications. Of the segmental aneuploidies, 63.6% (14/22) ≤5 Mb were de novo, and 50.0% (7/14) of de-novo segmental aneuploidies were pathogenic/likely pathogenic (P/LP) copy number variations, accounting for 0.7% of 963 blastocysts. For blastocysts carrying ≤5 Mb segmental aneuploidies, a re-analysis of back-up biopsy samples showed that 35.7% of de-novo segmental aneuploidies (5/14) were not detected in the back-up samples. Cases were reported in which prenatal diagnosis (amniocentesis) revealed the absence of embryonic ≤5 Mb segmental aneuploidies detected at the blastocyst stage.

Conclusions: The incidence of P/LP de-novo ≤5 Mb segmental aneuploidies in human blastocysts is extremely low. There is no compelling need to increase the resolution of PGT-A to 5 Mb in routine clinical practice.