Terminalogy 2

Sporadic research reports continued to investigate egg freezing principally in animal models, and occasionally in the human. However, these reports tended to underline the complications and lack of consistency between cross-species comparisons. For example, while the mouse can be a useful model it must be remembered that its eggs are only just over half the volume of the human egg, and this can have a major impact on the approach to cryopreservation in these two very different species cell types. Eventually though, driven by a series of papers published by an Australian researcher called Debbie Gook from Melbourne, clinical application of egg cryopreservation began to find favor by the middle of the nineties.Recently then, the early successes have been reproduced by others in both Italy and the USA giving rise conservatively to 10 babies from the freezing of women’s own eggs. Also at least one other baby has arisen from a clinical circumstance that is not completely unfamiliar to IVF clinics. n this case eggs had been collected during a routine IVF case, but no sperm were retrievable for insemination. So the oocytes were frozen, and donor semen was selected for a later IVF attempt. Ultimately both sets of gametes were thawed and used in a bsequent IVF procedure, which achieved a health delivery. This rather specific area of plication is of great potential benefit to infertile couples undergoing IVF
therapy where perhaps problems arise unexpectedly necessitating a halt to treatment prior to insemination of the eggs with sperm. For example, in another actual situation where an IVF couple suffered an untimely death in the family at the time of their procedure, they then chose to freeze all the eggs that had been retrieved until such time as they felt able to move forward with their therapy.All of these pregnancies and reports arose from work with frozen-thawed mature oocytes , but for one notable exception, where a pregnancy arose from an immature germinal vesicle (GV) stage egg. This may not sound to be of such great importance, but it could be that this stage of egg development may prove to be a more successful approach for egg cryopreservation. Such “young” eggs are approximately one to two days away from full maturity, and as such require further growth in the laboratory in culture after thawing. They currently appear as a by-product of less than optimal ovarian stimulation for IVF where not all eggs collected are mature. However, they survive
freezing well, and possess certain features that help to maintain their integrity during the rigors of cryopreservation. For example, their membranes are more permeable to the cryoprotectant (“antifreeze”), and their chromosomes are more conveniently and safely packaged in the nucleus protecting them from disruption. Such eggs, however, still have to undergo nuclear breakdown and full maturation before they can be fertilized, and therefore their developmental competency is not so clearly established as with fully mature oocytes that are frozen. The source of
these GV eggs, and whether they have been exposed to any external hormones may play a key role in the competency of these eggs. Harvesting of these eggs and the conditions for maturation remains to be resolved fully. But provisional studies in this area
are the first to lend credence to the possibility that immature follicles and the immature eggs inside isolated from ovarian tissue, may one day be fully grown in the laboratory outside of the body.How does Cryopreservation work, and what are the