Chromosome analysis of human preimplantation embryos.

Although karyotyping is the ideal method for diagnosing chromosome anomalies in the human embryo, the detection of chromosome anomalies in preimplantation human embryos by classical cytogenetics is extremely difficult. Nowadays, fluorescent in situ hybridization (FISH) in interphase nuclei is the method of choice. Both karyotype studies and FISH analysis of human preimplantation embryos obtained after in vitro fertilization (IVF) treatment revealed a high rate (25-51%) of chromosomally abnormal embryos. FISH analysis showed that chromosome mosaicism (22-24%) and chaotic embryos (7-26%) were the most frequent chromosome anomalies. Therefore, it seems that natural selection may be the reason for the low implantation rates of human preimplantation embryos in IVF programs. Although it is not possible to carry out such studies on embryos from natural conceptions, frequent occurrence of chromosome mosaicism and chaotically dividing embryos may apply to in vivo conception and explain the low fecundity rates in humans.