Intracytoplasmic sperm injection allows fertilization and development of achromosomally balanced embryo from a binovular zona pellucida

A binovular zona pellucida was found in two in-vitro fertilization (NF) tre atment cycles, In both cases, two oocytes of slightly unequal size were enc losed within a single zona pellucida, the larger oocyte appearing as a meta phase II oocyte while the smaller one as an immature oocyte with a germinal vesicle. Intracytoplasmic sperm injection performed in the mature oocyte o f each pair led to normal fertilization and embryonic development in both c ases. Results of genetic analysis performed by fluorescence in-situ hybridi zation in one of the two treatment cycles were consistent with a diploid ch romosomal status of both the non-injected immature oocyte as well as the em bryo which developed following the microinjection. These results indicate t hat, in this case, the binovular zona pellucida was most probably created w hen granulosa cells failed to separate two distinct oocytes during follicul ar formation. It may also imply that selective fertilization of a single ma ture oocyte in a binovular zona pellucida by intracytoplasmic sperm injecti on can lead to the development of a chromosomally balanced embryo and can p revent the undesired consequences that may result if the two oocytes are fe rtilized in the course of standard IVF.