Purpose: The purpose of this study was to compare the confirmation rate of day-3 embryo biopsy (blastomere) and trophectoderm biopsy using array-comparative genomic hybridization (array-CGH) technology.
Methods: A blinded study was conducted to re-analyse 109 embryos previously diagnosed as chromosomally abnormal by array-CGH. Preimplantation genetic screening (PGS) was performed using array-CGH on day 3 (n = 50) or day 5 (n = 59). Partial chromosome gains or losses were excluded (n=6), and only whole chromosome aneuploidies were considered. Re-analysis of whole blastocysts was carried out following the same array-CGH protocol used for PGS.
Results: The PGS result was confirmed in the whole blastocyst in (a) 49/50 (98 %) abnormal embryos after day-3 biopsy and (b) 57/59 (96.6 %) abnormal embryos after trophectoderm biopsy. One embryo (1/50; 2 %) was diagnosed as abnormal, with monosomy 18, on day 3, and software analysis of the whole blastocyst gave a euploid result; however, a mosaic pattern was observed for monosomy 18 in the whole blastocyst. Two trophectoderm biopsy cases (3.4 %) did not have the abnormalities (trisomy 7, and trisomy 1 and 4, respectively) verified in the whole embryo. Concordance rates for both biopsy strategies and for individual chromosomes were evaluated by Fisher's exact test and showed no significant differences.
Conclusions: Both types of biopsies showed similar high concordance rates with whole blastocyst results. Therefore, regarding the confirmation rates shown in this work, day-3 embryo biopsies can be representative of the whole embryo and both types of biopsy can be used for clinical analysis in PGS following the described array-CGH protocol.
Keywords: Array-CGH; Embryo biopsy; False-positive rate; Mosaicism; Preimplantation.