Abnormalities of sperm chromosome condensation in the cytoplasm of immature human oocytes.

This study analysed data from 27 couples in an IVF-ET programme. The maternal age range was 28-43 years. Statistical analyses on 182 oocytes showed no maternal age effect on the number of oocytes, their stage of maturation or their fertilization rate. There was also no effect of age of either partner or of seminal parameters on the fertilization rate. In contrast, occurrence of diploid oocytes was confined to three of the older women. The proportion of failures of fertilization was significantly higher in immature oocytes. These failures, which included 18 uncleaved, multipronuclear or fragmented zygotes, were related to disturbances of oocyte maturation. Four (out of five) oocytes re-inseminated with fresh semen produced polyspermy. One zygote showed marked asynchrony in the development of the two pronuclei. In eight zygotes the paternal complements had an allocyclic pattern of chromosome condensation between and within chromosomes or chromosome regions. In two other zygotes the paternal complement showed one chromosome prematurely condensed. This single-chromatid chromosome would be lost in the following cleavage division, suggesting that aneuploidy due to 'anaphase lag' is not a rare event during embryo cleavage.