Increased incidence of numerical chromosome abnormalities in spermatozoa injected into human oocytes by ICSI

The potential risk of transmitting chromosomally abnormal spermatozoa from infertile males into oocytes through intracytoplasmic sperm injection (ICSI ) has prompted us to investigate the male pronuclei of tripronuclear zygote s (3PN) obtained after ICSI. To specify the type of anomalies, we used trip le colour fluorescent in-situ hybridization (FISH) with three specific prob es for chromosomes X, Y and 18, From a total of 163 paternal complements of ICSI-3PN zygotes, 90 (55.2%) had Y-chromosome signals, Eighty-three of the se were normal, four had the disomy XY and three were diploid, In the remai ning 73 ICSI-3PN zygotes without Y-chromosome signals, the origin of patern al pronuclei was extrapolated through chromosome constitution of the first polar body. Five anomalies were found in this group of zygotes, giving a to tal rate of numerical chromosome aberrations for fertilizing spermatozoa of 7.4%, In contrast to ICSI, only two disomies (1.5%) were found in the cont rol group of IVF-3PN zygotes. Compared with the incidence of chromosome ano malies between paternal-derived pronuclei of ICSI- and IVF-3PN zygotes, the difference was statistically significant (P < 0.025), This study provides the first direct evidence of a higher incidence of numerical chromosome ano malies in sperm-fertilized human oocytes after ICSI.