Cytogenetic analysis of the oocyte and embryo after removal of the zona pellucida following failed fertilization

Cytogenetic analysis of the oocyte and embryo after removal of the zona pellucida provides a simple screening method for examining the oocyte and embryo and considering the morphological abnormalities of the zona and adjacent formations, cytoplasm and nucleus. Seventy-one unfertilized oocytes and 27 embryos with poor morphology or cleavage arrest were studied after fixation, staining and mechanical removal of the zona. Fixation was done with a glutaraldehyde solution (1%). The oocytes and embryos were then stained, causing weakening of the zona. A slight pressure on the cover slide led to rupture of the zona and the exposure of the oolema. The oocytes and embryos were analyzed for sperm attachment to and penetration through the zona, appearance of the polar bodies, differentiation of blastomeres from cytoplasmic fragments, nuclear status - pyknotic non-analyzable form, chromosomes or different degenerative appearances of DNA. Peeling of the zona is an easy and reliable screening technique needing only an ordinary light microscope. It provides the advantage of observing the whole structure of the oocyte-embryo, not just the chromosomes as in classical cytogentic methods.