Chromosome mosaicism in day 3 aneuploid embryos that develop to morphologically normal blastocysts in vitro

In all, 143 human embryos obtained 3 days (day 3) after insemination or int racytoplasmic sperm injection (ICSI) were biopsied and a single nucleated c ell removed for identification of aneuploidy by fluorescent in-situ hybridi zation (FISH) for chromosomes X, Y, 13, 16, 18 and 21, Fifty-one per cent o f embryos were aneuploid and significantly more aneuploid embryos blocked i n further development to morulae and blastocysts than euploid embryos (59 v ersus 34%; P < 0.001). Chromosomal analysis of the generated blastocysts re vealed 40% were aneuploid (16 of 40 generated blastocysts). Re-examination of cells by FISH for the same chromosome probes of the inner cell mass (ICM ) of expanded and hatching blastocysts derived from the aneuploid embryos r evealed a high incidence of mosaicism of ICM cell lineages that were usuall y predictable from observations of day 3 single-cell biopsies, These data w ould not support the hypothesis of a preferential allocation of euploid cel ls to the ICM and aneuploid cells to the trophectoderm, A high concordance between day 3 aneuploidy diagnosis and ICM cell lineages was observed with trisomies (97%), and multiple complex chromosome numerical abnormalities (1 00%), A reduced concordance was observed with monosomies (65%) and haploidy (18%), Concomitantly, the proportion of ICM cell lineages was increased in blastocysts whose chromosomal condition was diagnosed as haploid (21%) or with complex numerical abnormalities (50%).