VITRIFICATION
Freezing Embryos and Oocytes: About 20% of all offspring born worldwide from IVF cycles are from oocyte and embryo cryopreservation. Ice crystals should never be allowed to appear and grow inside the cells of the embryo and two basic approaches were developed:
A) Controlled slow-rate freezing
B) Vitrification protocol
Main Principles of Cryopreservation
1. Initial exposure to cryoprotectant (intracellular water has to be removed)
2. Cooling* (slow / rapid) to subzero temperature (-196°C)
3. Storage
4. Thawing or Warming (slowly or rapidly)
5. Dilution and removal of the cryoprotectant agent and replacement of the cellular and intracellular fluid at precise rate
6. Return to a physiological environment
*Embryos can be successfully cryopreserved by being cooled slowly (0.3°C/min) or rapidly (³ 10,000°C/min)
VITRIFICATION
Vitification is not a new technique and practised widely in other parts of the world but only now is it gaining popularity in the west.
Vitrification, or achieving a glass-like state (-130°C for water), was first described as a potential alternative to slow freezing in 1985. Since chilling injury to oocytes is time dependent, the rationale is to prevent ice formation and injury by cooling at a rate fast enough to solidify the intracellular water before it can crystallize.
Human eggs have high water content and are therefore extremely fragile and sensitive to all freezing procedures.
Controlled rate slow-freezing methods do not always succeed because they allow some intra-cellular ice crystal formation that causes some damage to embryos, and severe damage to most eggs, render them unusable. However, vitrification avoids the damage caused by crystal formation inside the cell increasing dramatically their survival rate.
Healthy children have already been born after insemination of vitrified oocytes.
Another advantage of vitrification is that it is possible to observe the entire procedure in the laboratory.
Pictures of the vitrification Method
