Effect of in vitro maturation before and after bovine immature oocyte vitrification in relation to oocytes quality and aneuploidy incidence

Abstract

Introduction: 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. Objective: 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, it means, cryopreservation (cryo) of immature oocytes followed by in vitro maturation (IVM) or in vitro maturation and cryopreservation of mature oocytes. Subjects and Methods: Cow ovaries will be used to retrieve oocytes, for this purpose all visible follicles within two to eight millimeters with good vascularization and clear follicular fluid will be aspirated using a thin needle. All the immature oocytes will be selected, according to the ooplasma and cumulus oophorus cells aspect, and divided into three groups to in vitro maturation or cryopreservation by vitrification. The first group will be composed only by immature oocytes which will be evaluated without intervention (no cryo and no IVM) and will be the control group (CG); the second group will be constituted by immature oocytes which will be cryopreserved, thawed after seven days and subsequently submitted to IVM (Group I), evaluations will be done after freezing-thawing (Group IA) and after in vitro maturation (Group IB). Finally the third group will include immature oocytes maturated in vitro for 24 hours and than cryopreserved and thawed after seven days (Group II), being evaluated after IVM (Group IIA) and freezing-thawing (Group IIB). The proposed evaluation is morphology and aneuploidy incidence, for this purpose optic microscopy, polarization microscopy and acetic-orcein technique will be used.