Premature chromosome condensation of the sperm nucleus after intracytoplasmic sperm injection.

A cytogenetic-cytological study was performed on unfertilized human oocytes (first polar body visible) after intracytoplasmic sperm injection (ICSI) with respect to the rate of prematurely condensed sperm chromosomes (G1-PCC). Out of 163 prepared oocytes derived from 41 ICSI cycles, 133 (approximately 82%) could be analysed successfully. a total of 60 oocytes (45.1%) showed metaphase II chromosomes in the haploid range 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 (28.4%) exhibited the maternal metaphase II chromosomes as well as G1-PCC of the sperm nucleus showing a remarkable variation in the degree of condensation. Ten ICSI cycles (each followed by an embryo transfer) were characterized each by 2-3 oocytes demonstrating G1-PCC. It is concluded that the main cause of failed fertilization after ICSI is the failure of oocyte activation. When the sperm 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 ejection of the spermatozoon in the perivitelline space except for two cases in which fertilization might have occurred. Finally, the observation of both a single chromatin region (n = 6) or two chromatin regions (n = 2) indicated oocyte activation which, however, was followed by developmental arrest.