Fertilization failures and abnormal fertilization after intracytoplasmic sperm injection

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Abstract
This study addresses the incidence of failed (0%) and suboptimal (50% fertilization in every cycle. Only 26% of the couples had 50% variation. The causes of failed and abnormal fertilization were studied in unfertilized and abnormally fertilized oocytes after staining with Hoechst 33342. In total, 1005 unfertilized oocytes were 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 principal cause of fertilization failure. A similar pattern was observed in activated, unfertilized oocytes, although there was a higher incidence of intact spermatozoa in these oocytes compared with metaphase II, unfertilized oocytes. Interestingly, 56% of the activated oocytes contained a decondensed sperm head which was not processed into a male pronucleus. A total of 169 abnormally fertilized oocytes was also studied. Two anomalies were found: digyny due to retention of the second polar body and its subsequent transformation into a third pronucleus, and abnormal pronuclear size and number.

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