LAUSR

OBJECTIVE To determine how often the results of a single trophectoderm (TE) biopsy tested by PGTseq, a targeted next-generation sequencing preimplantation genetic testing for aneuploidy technology, reflect the biology of the rest of the embryo. DESIGN Blinded prospective cohort study. SETTING University-affiliated private practice. PATIENT(S) A total of 300 blastocysts were donated; 113 of these embryos were euploid; 163 embryos possessed at least one whole chromosome aneuploidy; and 24 embryos were negative for whole chromosome aneuploidy but possessed at least one secondary finding on initial TE biopsy. INTERVENTION(S) All blastocysts underwent rebiopsy and preimplantation genetic testing for aneuploidy on the PGTseq platform. MAIN OUTCOME MEASURE(S) Partial concordance rate per embryo, total concordance rate per embryo, and total concordance rate per chromosomal event. RESULT(S) An initial TE biopsy result of euploidy or whole chromosome aneuploidy was reconfirmed in >99% of rebiopsied samples, affirming that meiotic errors are manifested in almost the entire embryo. In contrast, results of whole chromosome or segmental mosaicism were confirmed in 15%-18% of subsequent rebiopsies, suggesting that mitotic events are only sporadically seen throughout the embryo. Segmental aneuploidy was confirmed in 56.6% of rebiopsied samples, identifying a mixed meiotic and mitotic etiology for such abnormalities. CONCLUSION(S) A euploid or aneuploid result on the PGTseq platform is highly concordant with the rest of the embryo's ploidy status. The rarer confirmation of whole chromosome mosaic and segmental mosaic results suggest that these mosaics are suitable for embryo transfer. Segmental aneuploidy, with higher concordance rates throughout the embryo, may represent a different biologic etiology compared to mosaic embryos.