Preimplantation genetic diagnosis and chromosome analysis of blastomeres using comparative genomic hybridization

Numerical chromosome errors are known to be common in early human embryos and probably make a significant contribution to early pregnancy loss and implantation failure in IVF patients. Over recent years fluorescent in situ hybridization (FISH) has been used to document embryonic aneuploidies. Many IVF laboratories perform preimplantation genetic diagnosis (PGD) with FISH to select embryos that are free from some aneuploidies in an attempt to improve implantation, pregnancy and live birth rates in particular categories of IVF patients. The usefulness of FISH is limited because only a few chromosomes can be detected simultaneously in a single biopsied cell. Complete karyotyping at the single cell level can now be achieved by comparative genomic hybridization (CGH). CGH enables not only enumeration of all chromosomes but gives a more complete picture of the entire length of each chromosome and has demonstrated that chromosomal breakages and partial aneuploidies exist in embryos. CGH has provided invaluable information about the extent of mosaicism and aneuploidy of all chromosomes in early human conceptuses. CGH has been applied to clinical PGD and has resulted in the birth of healthy babies from embryos whose full karyotype was determined in the preimplantation phase.