Influence of in vitro maturation of bovine oocytes before or after vitrification on the morphology, incidence of aneuploidy and fertilization potential

Abstract

Oocyte cryopreservation necessarily demands ovarian hyperstimulation with gonadotrophins in order to maximize de number of recruited oocytes. Thus, young cancer patients there are going to be submitted to chemotherapy, a potentially sterilizing treatment, need to postpone their oncological treatment if they want to be submitted to a fertility preservation programme, which may include oocyte and/or embryo cryopreservation. A possible alternative that have been proposed to minimize the time of induction and reduce costs is to retrieve immature oocytes and submit them to in vitro maturation usually before cryopreservation. The aim of this study was to evaluate which sequence of procedure, considering in vitro maturation and cryopreservation, presents better results in terms of fertility preservation in a bovine oocytes model. Cow ovaries will be used to retrieve oocytes for this purpose. All the immature oocytes (VG) will be selected and divided into three groups to in vitro maturation or cryopreservation by vitrification. The first group (GI) will be composed only by immature oocytes which will be evaluated without intervention (no cryo and no IVM) and will be the control group; the second group (GII) will be constituted by immature oocytes which will be cryopreserved, thawed after seven days and subsequently submitted to IVM. Finally the third group (GIII) will include immature oocytes maturated in vitro for 24 hours and than cryopreserved and thawed after seven days, being evaluated after IVM and freezing-thawing. Evaluations will be done after freezing-thawing and after in vitro maturation The proposed evaluation is morphology, integrity of the zona pellucida and aneuploidy incidence, for these purpose optic microscopy, polarization microscopy and cytogenetics technique (Fluorescent in situ hibridization (FISH)) will be used. (AU)