title: The rate of blastocysts production following vitrification with step-wise equilibration of immature mouse oocytes.
abstract: BACKGROUND
  Cryopreservation and in vitro maturation (IVM) of oocyte is becoming an important technique in infertility treatment and fertility preservation. Also it has been proposed to establish a genetic resource bank for endangered or commercially important animal species.
  
  
  OBJECTIVE
  The aim of this study was to evaluate viability, maturation and fertilization rate of mouse immature oocytes after single and stepwise vitrification procedure.
  
  
  METHODS
  Oocytes were obtained from 4 weeks old female mice 48h after intraperitoneal injection of 7.5 IU pregnant mare serum gonadotropin (PMSG). Collected oocytes before vitrification were exposed to cryoprotectant, which was composed of 30% (v/v) ethylene glycol, 18% (w/v) Ficoll-70, and 0.3 M sucrose, either by single step or in a step-wise way. After vitrification and storage in liquid nitrogen, the oocytes were warmed and washed two times in medium TCM199 and then subjected to IVM, fertilization and subsequent development to blastocysts.
  
  
  RESULTS
  The oocytes survival rates after vitrifying-warming (88.96%), maturation rate (73.23%), the capacity of fertilization (57.80%) and embryonic development to blastocyst (16.41%) in the step-wise exposure were significantly higher (p<0.001) compared with corresponding rate in the single step procedure.
  
  
  CONCLUSIONS
  The results suggest that vitrification with step-wise procedure has positive effects on maturation and developmental capacity of mice germinal vesicle oocytes in compare with single step vitrification procedure.
authors.affiliation: Cellular and Molecular Research Center, Yasuj University of Medical Sciences, Yasuj, Iran.
authors.forename: Reza
authors.initials: R
authors.lastname: Mahmoudi
authors.affiliation: Department of Anatomy and Infertility Centre, Qazvin University of Medical Sciences, Qazvin, Iran.
authors.forename: Farzad
authors.initials: F
authors.lastname: Rajaei
authors.affiliation: Department of Anatomy and Embryology, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Iraj
authors.initials: I
authors.lastname: Ragardi Kashani
authors.affiliation: Department of Anatomy and Embryology, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Mehdi
authors.initials: M
authors.lastname: Abbasi
authors.affiliation: Department of Anatomy and Embryology, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Fardin
authors.initials: F
authors.lastname: Amidi
authors.affiliation: Department of Anatomy and Embryology, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Aligholi
authors.initials: A
authors.lastname: Sobhani
authors.affiliation: Research Center for Endometr and Endometriosis, Hamedan University of Medical Sciences, Hamedan, Iran.
authors.forename: Iraj
authors.initials: I
authors.lastname: Amiri
keywords: Germinal Vesicle stage Oocyte; IVM; Mouse; Vitrification