title: Osmotic-shock produced by vitrification solutions improves immature human oocytes in vitro maturation.
abstract: BACKGROUND
  During cytoplasmic oocyte maturation, Ca(2+) currents are vital for regulating a broad range of physiological processes. Recent studies have demonstrated that DMSO and EG cause large transient increases in intracellular Ca(2+) in mouse oocytes. The CP used in vitrifying protocols also increases the intracellular calcium transient. The aim of this study is to evaluate the effects of vitrifying time (before and after IVM) and exposure to the vitrification solutions and ionomycin on oocyte quality and embryonic development.
  
  
  METHODS
  221 GV-oocytes unsuitable for IVF-ICSI cycles were randomly distributed into one of the following three groups. G1 (control group): 41 GV-oocytes IVM until MII; G2: 43 oocytes vitrified at GV stage and IVM until MII stage; and G3: 53 GV-oocytes IVM until MII and then vitrified. In order to clarify the effect of vitrification solutions (VS) on human oocyte IVM through the intracellular Ca(2+) oscillation, the following two groups were also included. G4: 43 GV-oocytes exposed to VS and IVM until MII; and G5: 41 GV-oocytes exposed to ionomycin and IVM until MII. All GV-oocytes that reached MII-stage were parthenogenetically activated to assess oocyte viability. IVM was performed in IVF-medium (24-48 h). Chemical treatment (ionomycin) and osmotic treatment (vitrification solutions) were performed without liquid-N2 immersion. The following rates were evaluated: survival (SR), in-vitro maturation (IVMR), activation (AR), development to 2-cell (DRC), development to morula (DRCM) and development to blastocyst (DRB). Ratios between the different treatment groups were compared using contingency tables analysis (chi-square test).
  
  
  RESULTS
  A high survival rate was obtained in G2 (95.5 %) and G4 (96.6 %). In-vitro maturation rate was significantly higher for G4 (86 %) and G2 (83.7 %) compared to G1 (63.4 %), G3 (56.6 %) and G5 (48.8 %). DRCM was significantly higher for G1 and G2 compared to G3 (G1: 15.8 %, G2: 20.7 % and G3: 0 %). DRB was only obtained for the oocytes vitrified before IVM (G2: 3.4 %). AR was also significantly higher for G2 and G4 compared to G5 (G2: 80.5 %, G4: 86.5 % and G5: 55 %). DRCM and DRB were only obtained in G2 and G4. DRCM was significantly higher for oocytes vitrified at GV stage (G2) and for oocytes exposed to the VS in G4 compared to the oocytes exposed to the ionomycin in G5 (G2: 20.7 %; G4: 37.5 % and G5: 0 %).
  
  
  CONCLUSIONS
  Vitrifying GV-oocytes improves their IVM. Further investigation could look to increase the oocyte pool and improve fertility preservation options.
authors.affiliation: Unidad de Reproducción Humana, Área de Salud de la Mujer, Hospital Universitario y Politécnico La Fe, Valencia, Spain.
authors.forename: Inmaculada
authors.initials: I
authors.lastname: Molina
authors.affiliation: Unidad de Reproducción Humana, Área de Salud de la Mujer, Hospital Universitario y Politécnico La Fe, Valencia, Spain.
authors.forename: Judith
authors.initials: J
authors.lastname: Gómez
authors.affiliation: Departamento de Estadística e Investigación Operativa Aplicadas y Calidad, Universidad Politécnica de Valencia, Valencia, Spain.
authors.forename: Sebastián
authors.initials: S
authors.lastname: Balasch
authors.affiliation: Fundación Instituto Valenciano de Infertilidad, Instituto Universitario IVI, Valencia, Spain.
authors.forename: Nuria
authors.initials: N
authors.lastname: Pellicer
authors.affiliation: Unidad de Genética, Torre A planta 4º, Hospital Universitario y Politécnico La Fe, Avenida de Fernando Abril Martorell, nº 106, 46026, Valencia, Spain. edurnenovella@yahoo.es.|Grupo de investigación de Medicina Reproductiva, Instituto de Investigación Sanitario La Fe, Valencia, Spain. edurnenovella@yahoo.es.
authors.forename: Edurne
authors.initials: E
authors.lastname: Novella-Maestre
mesh_terms: D000328:Adult; D002118:Calcium / Q000378:metabolism; D002470:Cell Survival; D003470:Culture Media; D047108:Embryonic Development; D005260:Female; D059247:Fertility Preservation; D006801:Humans; D059471:In Vitro Oocyte Maturation Techniques / Q000379:methods*; D009865:Oocytes / Q000254:growth & development*; D009997:Osmotic Pressure; D058989:Vitrification
chemical_list: D003470:Culture Media; D002118:Calcium
keywords: Contingency tables; Fertility preservation; Immature oocytes; In vitro maturation; Vitrification