The cytogenetic analysis of human zygotes and preimplantation embryos.

A review of cytogenetic studies on human zygotes and preimplantation embryos is presented. This survey documents the high incidence of chromosomal abnormalities in embryos in vitro. Up to date, 914 zygotes and embryos have been karyotyped. The rate of abnormalities is significantly higher in morphologically poor-quality embryos than in good-quality embryos (86.6 and 36.6% respectively). In both groups, aneuploidy is the most frequently observed abnormality. In addition, various types of aberrations such as polyploidy, haploidy, mosaicism or fragmentation are also found. Among tripronucleated zygotes, 81.9% display chromosomal abnormalities. Data suggest that some parameters of IVF procedures might be responsible for the occurrence of some abnormalities.