Chromosome anomalies in human oocytes failing to fertilize after insemination in vitro.

Three-hundred-and-two unfertilized oocytes left over from successful in-vitro fertilization (IVF) attempts in 143 women (27-42 years) on a follicular stimulating hormone-human menopausal gonadotrophin (FSH-HMG) stimulation regime were subjected to chromosome analysis. Ten oocytes were degenerated with no visible chromosomes and 41 metaphases had chromosomes that were clumped together which could not be interpreted either numerically or structurally. Of the remaining oocytes, 76.6% (192/251) had a normal haploid complement (n = 23), 13% (33/251) were hypohaploid (n = 19-22), 8% (20/251) were hyperhaploid (n = 24-26), 2% (5/251) were diploid (2n = 46) and 0.4% (1/251) had structural rearrangements. The 21% aneuploidy was from 24 different patients and hypohaploid sets had chromosomes missing mainly from the A, B, C, D and G groups while the hyperhaploid sets had extra chromosomes from A, B, D, G and E groups of the human karyotype. The mean age of patients showing aneuploid oocytes was 36.7 years which was above the mean for the entire group. The aneuploidy may have been brought about by errors in oogenesis (anaphase lagging or non-disjunction) and may offer one explanation for fertilization failure and overall low pregnancy rates after IVF.