Assessment of aneuploidy concordance between clinical trophectoderm biopsy and blastocyst

Abstract STUDY QUESTION Is a clinical trophectoderm (TE) biopsy a suitable predictor of chromosomal aneuploidy in blastocysts? SUMMARY ANSWER In the analyzed group of blastocysts, a clinical TE biopsy was an excellent representative of blastocyst karyotype in cases of whole chromosome aneuploidy, but in cases of only segmental (sub-chromosomal) aneuploidy, a TE biopsy was a poor representative of blastocyst karyotype. WHAT IS KNOWN ALREADY Due to the phenomenon of chromosomal mosaicism, concern has been expressed about the possibility of discarding blastocysts classified as aneuploid by preimplantation genetic testing for aneuploidy (PGT-A) that in fact contain a euploid inner cell mass (ICM). Previously published studies investigating karyotype concordance between TE and ICM have examined small sample sizes and/or have utilized chromosomal analysis technologies superseded by Next Generation Sequencing (NGS). It is also known that blastocysts classified as mosaic by PGT-A can result in healthy births. TE re-biopsy of embryos classified as aneuploid can potentially uncover new instances of mosaicism, but the frequency of such blastocysts is currently unknown. STUDY DESIGN, SIZE, DURATION For this study, 45 patients donated 100 blastocysts classified as uniform aneuploids (non-mosaic) using PGT-A by NGS (n = 93 whole chromosome aneuploids, n = 7 segmental aneuploids). In addition to the original clinical TE biopsy used for PGT-A, each blastocyst was subjected to an ICM biopsy as well as a second TE biopsy. All biopsies were processed for chromosomal analysis by NGS, and karyotypes were compared to the original TE biopsy. PARTICIPANTS/MATERIALS, SETTING, METHODS The setting for this study was a single IVF center with an in-house PGT-A program and associated research laboratory. MAIN RESULTS AND THE ROLE OF CHANCE When one or more whole chromosomes were aneuploid in the clinical TE biopsy, the corresponding ICM was aneuploid in 90 out of 93 blastocysts (96.8%). When the clinical TE biopsy contained only segmental (sub-chromosomal) aneuploidies, the ICM was aneuploid in three out of seven cases (42.9%). Blastocysts showing aneuploidy concordance between clinical TE biopsy and ICM were also aneuploid in a second TE biopsy in 86 out of 88 cases (97.7%). In blastocysts displaying clinical TE-ICM discordance, a second TE biopsy was aneuploid in only two out of six cases (33.3%). LIMITATIONS, REASONS FOR CAUTION All embryos in this study had an initial classificatio