Re-analysis of whole blastocysts after trophectoderm biopsy indicated chromosome aneuploidy.

BACKGROUND: To compare the concordance between trophectoderm (TE) analysis and whole blastocyst analysis of embryos from chromosomal structural rearrangement (SR) carriers. METHOD: Sixty-three abnormal blastocysts identified by preimplantation genetic testing for chromosomal structural rearrangement (PGT-SR) were included. The whole blastocysts were processed through multiple displacement amplification cycle and sequenced for 24-chromosome aneuploidy screening by next-generation sequencing (NGS). The sequencing results were compared with those of TE biopsy from the same blastocysts and the primary chromosomal rearrangement of the couples. RESULTS: Analysis of the 63 blastocysts showed 68% (43/63) complete concordance between TE sequencing analysis and whole blastocyst results. Approximately one third (20/63, 32%) of the sequencing results showed some level of discordance between the two samples. Of these, 14% (9/63) of the embryos were identified as euploid after whole blastocyst sequencing. Among them, seven blastocysts were classified as chromosome mosaicism (five whole chromosomes, two segmental) after TE analysis, while two displayed non-SR related segmental changes in the TE biopsy. Of the original analyses, 70% (44/63) of findings were associated with the primary parental chromosomal rearrangement, while 30% (19/63) had no association. CONCLUSIONS: TE biopsy with NGS for PGT-SR is an efficient strategy to identify embryos suitable for transfer. While there was a high concordance between TE and whole blastocyst chromosome results, some embryos classified as mosaic in the original analysis and therefore unsuitable for transfer were reclassified as chromosomally balanced. To maximize the number of embryos available for PGT-SR patients, we suggest that embryos with mosaic non-SR chromosomal rearrangement should be stored and considered for transfer after appropriate counseling.