TECHNICAL AND PHYSIOLOGICAL-ASPECTS ASSOCIATED WITH THE LOWER FERTILIZATION FOLLOWING INTRA CYTOPLASMIC SPERM INJECTION (ICSI) IN HUMAN

The fertilization rates with ICSI range from 30% to 70% and suggest th at, despite injecting sperm into mature oocytes, significant fertiliza tion failure still occurs in humans. The objective of this study was t o determine technical and physiological factors which may contribute t o lower fertilization following ICSI. Eggs that failed to show two pro nuclei (PN) 48 hours after ICSI were studied at two different time int ervals: at ICSI program inception (group A) and after 8 months (group B). The eggs were analyzed by staining with DNA fluorochromes, Hoescht 33258 and DAPI. The extent of sperm head as well as maternal chromati n decondensation in unfertilized ICSI eggs was determined by high reso lution fluorescence microscopy. The average fertilization rate (FR) fr om all ICSI cycles in these two groups was 45%. The FR in Groups A and B were 35% and 59%, respectively (P < 0.05). In Group A, 65% of the u nfertilized eggs were characterized by condensed sperm chromatin with 11% showing partial decondensation. In Group B, only 28% of the unfert ilized eggs demonstrated condensed sperm chromatin while 45% were part ially decondensed. Sperm chromatin was not detected in 24% of all unfe rtilized eggs studied. The maternal chromatin remained at metaphase II in 84% of all unfertilized eggs analyzed. These observations suggest that the technical problem of deposition of the sperm inside the egg i s not the major cause for failure of fertilization rates in ICSI cycle s. The increased percentage of eggs undergoing sperm head decondensati on may be related to subtle changes in technique as experience is gain ed over time. The failure of sperm head decondensation in some of the ICSI eggs may be associated with cytoplasmic immaturity but not nuclea r maturity. (C) 1998 by Elsevier Science Inc.