title: Fertilization rates are improved after IVF if the corona radiata is left intact in vitrified-warmed human oocytes.
abstract: BACKGROUND
  Before human MII oocytes are vitrified they are usually denuded from their cumulus cells. In this study we wanted to investigate the effects of an intact corona radiata on the vitrification and fertilization of human oocytes.
  
  
  METHODS
  The study comprised two different parts. In Part 1, 36 MII stage oocytes, from 6 patients, were randomly assigned into a control group, a group of vitrified-warmed oocytes without a corona radiata and a group of vitrified-warmed oocytes with an intact corona radiata. In each group of 12, 6 oocytes were used for evaluation of the zona pellucida solubility (hardening) and another 6 oocytes were used for the analysis of their ultrastructure. In addition, six polyspermically fertilized oocytes were used as positive controls for zona pellucida hardening. In Part 2, 16 patients in total produced 107 fresh and 98 vitrified-warmed oocytes, with or without an intact corona radiata. All oocytes were fertilized via conventional IVF and embryos were transferred according to our standard ET routines. The oocyte survival and fertilization rates, embryo quality and pregnancy and implantation rates were evaluated.
  
  
  RESULTS
  There were no differences in oocyte survival, zona pellucida solubility (hardening) or the number of cortical granules between the vitrified-warmed and fresh oocytes. There were also no differences in the zona pellucida solubility and the number of cortical granules between vitrified-warmed oocytes with or without an intact corona radiata. However, the oocytes with an intact corona radiata had a higher fertilization rate after conventional IVF insemination. No differences were seen in the survival and cleavage rates, the percentage of high-quality embryos or the clinical outcome.
  
  
  CONCLUSIONS
  Zona hardening and ultrastructural damage do not seem to occur in vitrified human oocytes. An intact corona radiata in vitrified-warmed oocytes retains their fertilization capacity in conventional IVF, but does not improve the embryo quality. Poor fertilizing capacities of vitrified-warmed oocytes without an intact corona radiata seem to have been due to the complete removal of the cumulus cells.
authors.affiliation: Reproductive Medical Centre of Anhui Provincial Hospital Affiliated to Anhui Medical University, Hefei 230001,  China.
authors.forename: Xian-Hong
authors.initials: XH
authors.lastname: Tong
authors.forename: Li-Min
authors.initials: LM
authors.lastname: Wu
authors.forename: Ren-Tao
authors.initials: RT
authors.lastname: Jin
authors.forename: Li-Hua
authors.initials: LH
authors.lastname: Luo
authors.forename: Hong-Bing
authors.initials: HB
authors.lastname: Luan
authors.forename: Yu-Sheng
authors.initials: YS
authors.lastname: Liu
mesh_terms: D000328:Adult; D002681:China / Q000453:epidemiology; D054885:Cumulus Cells / Q000502:physiology / Q000648:ultrastructure; D004624:Embryo Transfer; D005260:Female; D005307:Fertilization in Vitro; D006358:Hot Temperature; D006801:Humans; D059471:In Vitro Oocyte Maturation Techniques; D007247:Infertility, Female / Q000473:pathology / Q000503:physiopathology / Q000628:therapy*; D007248:Infertility, Male / Q000628:therapy*; D008297:Male; D046529:Microscopy, Electron, Transmission; D009865:Oocytes / Q000648:ultrastructure*; D011247:Pregnancy; D018873:Pregnancy Rate; D012995:Solubility; D013084:Sperm-Ovum Interactions; D058989:Vitrification; D015044:Zona Pellucida / Q000737:chemistry / Q000648:ultrastructure