FERTILIZATION FAILURES AND ABNORMAL FERTILIZATION AFTER INTRACYTOPLASMIC SPERM INJECTION

This study addresses the incidence of failed (0%) and suboptimal (< 50 %) fertilization after intracytoplasmic sperm injection (ICSI), variat ion in the ICSI fertilization rate for specific couples, and the cause s of fertilization failure and abnormal fertilization after ICSI. Fail ed fertilization occurred in only 37 of 1343 cycles (3%). The risk of failure was highest (37%) when only one oocyte was injected, and was l owest (0.8%) when five or more oocytes were collected. The incidence o f suboptimal fertilization and the variation in the fertilization rate were studied in 87 couples who each had three cycles of ICSI in which four oocytes were injected with ejaculated spermatozoa. Approximately 74% of these couples achieved > 50% fertilization in every cycle. Onl y 26% of the couples had < 50% fertilization in one or more cycles, an d most of these (17%) had only a single cycle with suboptimal fertiliz ation. Only four of the 87 couples (5%) had suboptimal fertilization i n all three cycles. The difference between the maximum and minimum fer tilization rate for a couple was used as an index of variation of the fertilization rate. It was found that 47 couples (54%) had 0-25% varia tion, 33 couples (38%) had 26-50% fertilization and only seven couples (8%) had > 50% variation. The causes of failed and abnormal fertiliza tion were studied in unfertilized and abnormally fertilized oocytes af ter staining with Hoechst 33342. In total, 1005 unfertilized oocytes w ere studied, of which 828 (82%) were still at metaphase II and 177 (18 %) were activated. Most of the oocytes (83%) contained a spermatozoon and, in the majority of these oocytes, the sperm head was partially or completely decondensed. Hence, failure of oocyte activation was the p rincipal cause of fertilization failure. A similar pattern was observe d in activated, unfertilized oocytes, although there was a higher inci dence of intact spermatozoa in these oocytes compared with metaphase I I, unfertilized oocytes. Interestingly, 56% of the activated oocytes c ontained a decondensed sperm head which was not processed into a male pronucleus. A total of 169 abnormally fertilized oocytes was also stud ied. Two anomalies were found: digyny due to retention of the second p olar body and its subsequent transformation into a third pronucleus, a nd abnormal pronuclear size and number.