Slow Oocyte Freezing

The science of cryobiology and IVF have developed in parallel over the past 50 years. Artificial insemination on a large scale, only became possible with the pioneering work of Polge et al. (1949) who demonstraded that cells (in this case fowl semen) could be recovered in a viable state from very low temperature. Oocyte cryopreservation has been a much anticipated advance in human IVF and reproductive sciences that may extend female reproductive potential, while avoiding ethical and legal complications originating from the storage of embryos and fertilized oocytes. Although the chemical reactions of life can be suspended for an unlimited duration in simple biological organisms, the same is not true for organism with high level of complexity. Moreover, for any given complex life form, each constituent cell type has a certain degree of resistance which is, in every case, greater than that of the organism as a unit. General conditions for the preservation of ultrastructure and cellular function Resistance to cold and freezing depends on a number of different factors. In the first place, a form of thermal shock can occur both above and below the freezing point. Also, the formation of ice crystals both inside and outside cells can entail serious physical damage. Another consequence of ice formation is a change in the physical environment of the cells. The freezing of water results in increasing the concentration of salt in the solution; such an increase in electrolyte concentration leads to cellular dehydration.