Comprehensive chromosomal analysis of human preimplantation embryos using whole genome amplification and single cell comparative genomic hybridization.

Analysis of small numbers of chromosomes using interphase fluorescent in-situ hybridization (FISH) probes has revealed that 50% of human preimplantation embryos contain abnormal cells. Detection of high levels of mosaicism with so few probes has led some researchers to extrapolate that a full analysis of all 23 pairs of chromosomes would reveal that all human embryos contain a proportion of abnormal cells. However, existing cytogenetic protocols cannot achieve such an analysis due to technical limitations. We have developed a novel technique based on whole genome amplification and comparative genomic hybridization (CGH), which for the first time allows the copy number of every chromosome to be assessed in almost every cell of a cleavage-stage embryo. We have successfully analysed 64 cells (blastomeres) derived from 12 embryos and have detected unusual forms of aneuploidy, high levels of chromosomal mosaicism, non-mosaic aneuploidy and chromosome breakage. This is the first report of a comprehensive assessment of chromosome copy number in human embryos and indicates that, despite high levels of mosaicism, some embryos do have normal chromosome numbers in every cell. Such embryos may have a superior developmental potential, and their low frequency may explain correspondingly low success rates of natural and assisted conception in humans.