Vitrification of in vitro matured oocytes collected from surplus ovarian medulla tissue resulting from fertility preservation of ovarian cortex tissue

The aim of the study was to investigate the maturation rate of immature oocytes collected from ovarian medulla tissue normally discarded during preparation of ovarian cortical tissue for fertility preservation. Further we evaluated survival of derived MII oocytes following vitrification and warming. 36 patients aged from 8 to 41 years who had one ovary excised for fertility preservation were included. Oocytes were collected from the medulla tissue and matured in vitro 44–48 h followed by vitrification. Number of oocytes collected, the rates of maturation and post-warming survival were assessed. On average, 11 immature oocytes were collected per patient. The overall maturation rate was 29 % irrespective of whether the ovary was transported 4–5 h on ice or obtained immediately after oophorectomy. The maturation rate in patients below 20 years of age (55 %) was significantly higher than that of patients aged 20–30 years (29 %) and above 30 years (26 %). The post-warming survival rate was 64 %. No significant relationship was observed between the number of collected oocytes and the age of patients. Approximately three MII oocytes were obtained per patient following in vitro maturation (IVM) of immature oocytes collected from medulla tissue, of which two survived vitrification and warming. This approach represents an add-on method to potentially augment the fertility opportunity for cancer patients, especially in young women with cancer where transplantation of cortical tissue may pose a risk of relapse, but the IVM approach is currently too inefficient to be the only method used for fertility preservation.