A simple method for the morphological analysis of human ova: zona penetration in oocytes failing to fertilize or fertilizing abnormally in vitro

A simple and rapid technique is described whereby several unfertilized oocytes and embryos can be processed simultaneously for embedding and sectioning for histological analysis. Oocytes are encased in a serum matrix and thereafter can be handled with ease. A total of 112 unfertilized oocytes and abnormal embryos following insemination in vitro have been examined. Only 31% of oocytes showed pyknotic nuclei after a mean of 4.0 +/- 1.24 days in culture and 37% had recognizable metaphase II chromosomes. Twenty per cent showed evidence of fertilization, but spermatozoa had failed entirely to penetrate the zonae pellucidae of 34% of oocytes. The mean percentages of penetrating sperm were not significantly different between oocytes which did and did not fertilize. Under these in-vitro conditions, approximately 1-2% of spermatozoa reaching the oocyte penetrated into the zona pellucida and a lesser number to the perivitelline space. Polar bodies were also observed and the incidence of divisions, retention and parthenogenesis estimated. This technique may advance our understanding of the reasons for the success or failure of fertilization in vitro.