Supernumerary human preembryos provide potential for preimplantation genetic diagnosis.

Preimplantation genetic diagnosis is an alternative to the classical prenatal diagnosis for couples undergoing in vitro fertilization. It allows very early embryo selection--before the intrauterine embryo transfer. Prior to clinical application of preimplantation diagnosis in the Infertility Treatment Centre "Technobioassistance", Sofia Medical Faculty, we have developed preimplantation diagnosis models of human spermatozoa and untransferred 2-8-cell human embryos obtained in vitro. Directly fluorescein isothiocyanate-labelled probes specific for the centromeric regions of chromosomes 1, 5, 19 and X (Boehringer Mannheim) were used. Eighty-six point three percent of fixed blastomeres with normal size and shape had unfragmented nuclei with dispersed interphase chromatin or mitotic chromosomes and all of them demonstrated successful hybridization. In cases with more than 75% of embryo cells suitable for analysis we were able to estimate the presence of mosaicism among the blastomeres.