PREMATURE CHROMOSOME CONDENSATION OF THE SPERM NUCLEUS AFTER INTRACYTOPLASMIC SPERM INJECTION

A cytogenetic-cytological study was performed on unfertilized human oo cytes (first polar body visible) after intracytoplasmic sperm injectio n (ICSI) with respect to the rate of prematurely condensed sperm chrom osomes (G(1)-PCC). Out of 163 prepared oocytes derived from 41 ICSI cy cles, 133 (similar to 82%) could be analysed successfully, A total of 60 oocytes (45.1%) showed metaphase II chromosomes in the haploid rang e along with an intact sperm head and 27 oocytes (20.3%) were missing the sperm head, but two of them showed an approximately diploid set of chromosomes; 38 oocytes (28.6%) exhibited the maternal metaphase II c hromosomes as well as G(1)-PCC of the sperm nucleus showing a remarkab le variation in the degree of condensation, Ten ICSI cycles (each foll owed by an embryo transfer) were characterized each by 2-3 oocytes dem onstrating G(1)-PCC. It is concluded that the main cause of failed fer tilization after ICSI is the failure of oocyte activation, When the sp erm nucleus is able to act with the chromosome condensing factors and the oocyte does not become activated, this will lead to the induction of PCC. Absence of the sperm head might be due to injection or ejectio n of the spermatozoon in the perivitelline space except for two cases in which fertilization might have occurred, Finally, the observation o f both a single chromatin region (n = 6) or two chromatin regions (n = 2) indicated oocyte activation which, however, was followed by develo pmental arrest.