Oocyte Cryopreservation: The Impact of Cryopreservation on the Meiotic Spindle and Mitochondria of Human Oocytes.
Condition: Infertility
MeSH terms: Infertility
Study type: Observational

Summary: 
      Our aims is to document the possible effect of cryo- preservation at the meiotic spindle and
      mitochondrial levels.
    

Detailed description: 
      The cryopreservation of oocytes (OC) has broad applications in the field of reproductive
      endocrinology for the management of clinical problems in both fertile and infertile patients.
      For example, young fertile women who are diagnosed with malignancies may freeze their oocytes
      before initiating potentially toxic radiation or chemical cancer therapy which may render
      them sterile.

      Using the OC technology, we have established a frozen oocyte bank using healthy, compensated
      egg donors who have been pre- screened using FDA criteria. Following an appropriate
      quarantine time, oocytes can be thawed and offered to women diagnosed with premature ovarian
      failure or diminished ovarian reserve. This application of OC has already shown promise by
      eliminating the logistical and clinical complications associated with traditional oocyte
      donation using fresh oocytes from donors.

      From the societal perspective, cryopreservation of surplus oocytes in an IVF cycle may remove
      some of the social and moral objections surrounding embryo cryopreservation. Currently, our
      frozen oocyte pregnancy rate (56%) is equivalent to our frozen embryo pregnancy rate (45%).
      Patients, who have completed their families, find it easier to discard oocytes versus
      embryos.

      Finally, women who make a personal choice to delay childbearing may be offered the option to
      preserve their oocytes with the potential for later use.

      The two distinct techniques currently being used for oocyte cryopreservation are: 1)
      controlled-rate freezing and 2) vitrification. Controlled-rate freezing shares some
      similarities with the basic technology employed for embryo cryopreservation in nearly every
      IVF program. The technique involves the slow freezing of embryos in cryoprotectant solutions,
      often combined with a computer-controlled freezer to regulate temperature changes. Attempts
      to improve our understanding of oocyte cryobiology have been mostly empirical using trial and
      error. Only limited experience has been gained by adopting scientific models able to predict
      the effect of "cryo" stress imposed on oocytes using various freezing methods (Fuller and
      Paynter, 2004; Paynter, 2005). In the absence of properly designed studies, advances in
      clinical experience with oocyte freezing have been very limited. One of the major obstacles
      to the implementation of oocyte freezing had been the inability to achieve reproducible high
      survival rates owing to an important effect on the intracellular organelles. For example, due
      to its sensitivity at low temperature, the metaphase II spindle has always been considered
      susceptible to structural alterations which potentially might interfere with normal
      chromosome segregation at meiosis II. Additionally, the essential role of mitochondria in
      normal cell function, fertilization and early embryo development has previously been
      described (Jones et al., 2004).

      Our recently developed modified freeze-thaw protocol has consistently shown high recovery
      rates, leading to optimism that oocyte storage could at last become available in clinical
      practice. But it remains to be demonstrated that excellent post-thaw survival coincides with
      cellular integrity and unaltered developmental competence. Therefore, prior to recommending
      the adoption of oocyte cryopreservation, one of our aims is to document the possible effect
      of cryo- preservation at the meiotic spindle and mitochondrial levels. An important aim of
      our study is to assess the post-thaw viability and organelle integrity of oocytes using: 1) a
      conservative technique [PolScope analysis of meiotic spindle] and 2) a non-conservative
      technique [Fluorescence microscopy analysis of the meiotic spindle and mitochondria] using
      our oocyte cryopreservation protocol.

      Continuing development in freezing technology is occurring rapidly. It can be anticipated
      that in the near future, egg freezing will become as successful as embryo cryopreservation.
      Finally, as more clinical experience with egg freezing accumulates, acceptable outcome data
      will determine the future of egg freezing. Until then, oocyte cryopreservation should be used
      in carefully selected clinical cases with full disclosure to the patient regarding risks and
      limited success rates.
    

Observational model: Cohort
Time perspective: Prospective
Sampling method: Non-Probability Sample
Study population: 
        Women of reproductive age who undergo controlled ovarian hyperstimulation (COH) for IVF are
        recruited for this study.
      
Keywords: Oocyte Cryopreservation; Slow-Freeze; Egg Freezing; Meiotic Spindle; Mitochondria; Human Oocytes Freezing.