Chromosomal integrity of human preimplantation embryos at different days post fertilization

In order to investigate the dynamics of genomic alterations that occur at different developmental stages in vitro, we examined the chromosome content of human preimplantation embryos by molecular-cytogenetic techniques at the single-cell level, up to 13 days post fertilization. The embryos were genetically analyzed several times during their development in culture; each embryo was first analyzed by FISH at 'Day 3' post fertilization, than during its growth in vitro and the third analysis was performed at development arrest, then the entire blastocyst was analyzed by comparative genomic hybridization (CGH/aCGH). We found that while on 'Day 3' only 31 % of the embryos were detected as normal, on 'Day 5-6', 44 % of the embryos were classified as normal and on 'Day 7', 57 % were normal. On 'Days 8-13', 52 % of the embryos were classified as chromosomally normal. One third of the embryos that were chromosomally abnormal on 'Day 3', were found to be normal at development arrest point. These dynamic changes that occur at early developmental stages suggest that testing a single blastomere at 'Day 3' post fertilization for PGD might inaccurately reflect the embryo ploidy and increase the risk of false aneuploidy diagnosis. Alternatively, blastocyst stage diagnosis may be more appropriate.