Chromosome analysis of human oocytes failing to cleave after insemination in vitro.

Seventy-six human oocytes lacking signs of fertilization 48 h after insemination in vitro were fixed for chromosome analysis. Only one out of 61 oocytes showed mitotic chromosomes indicating fertilization. Thus, non-cleavage is almost synonymous with non-fertilization. Chromosomes in second meiosis were found in 60 oocytes, of which 52 (86.7%) were analysable. Of these, only 18 (34.6%) displayed an apparently normal 23,X karyotype. Fifteen preparations showed no chromosomes at all but some contained small nuclei, most likely due to degeneration. An earlier stage of degeneration could be represented by a group of second meiosis oocytes (20.0%) carrying between 10 and 18 chromosomes. The large proportion of chromosome abnormalities in this sample might have been due to the fact that the oocytes were unfertilized and perhaps that abnormal oocytes had matured due to ovarian stimulation.