Effect of vitrification on viability of human immature oocytes at different stages

Abstract

There has been a steady raise in the survival rate of female cancer patients with advances in oncology and anti-cancer therapy. The radiation and chemotherapy regimes were reported to induce premature ovarian failure, causing the patient infertile. Thus there has been a greater needs for options to preserve the reproductive potential of these individuals. A study by Chian et al in 2004 reported pregnancies and live births resulted from immature oocytes and subjected to in vitro maturation (IVM) showed that immature oocytes might be compotetent for a full-term development after IVM and fertilization. This discovery has caused great excitement and an increase in research into immature oocyte cryopreservation as a potential option for fertility preservation. This investigation aims to explore the potential of immature oocyte vitrification by initial experiment on viability in order to overcome disadvantages of embryo and mature oocyte cryopreservation. In this study, a total of 242 human immature oocytes were divided into 3 groups based on their nuclear status and went through vitrification. The viability of three groups after vitrification was compared and the evaluation based on morphological parameters and Trypan exclusion assay. The survival rates after vitrification were 78.83% for Germinal Vesicle (GV), 55.36% for GV- break down (GVBD) and 44.90% for Metaphase I (MI) oocytes. They contributed a rate of 66.53% for immature oocyte viability after vitrification. Results showed that oocytes at GV stage achieved a significantly better viability than other stages (P<0.01) while the GVBD and MI oocytes were not statistically different in survival rates (P>0.05). GV oocytes appeared to be more resistant than other immature stages to vitrification. This also implied that vitrification was a reliable method for GV oocyte cryopreservation and GV should be selected among immature oocyte stages in order to achieve better viability after going through vitrfication procedure.

Keywords: Vitrification Immature oocytes Oocyte cryopreservation