A woman will undergone controlled ovarian hyper-stimulation to increase the number of follicles growing on the ovaries, this will maximise the number of eggs available for retrieval. Every woman is different and responds differently to treatment so the number and quality of eggs harvested will vary. Once the eggs have been collected the support cells around the eggs are removed. At this time the maturity of the eggs are determined. Only mature eggs are suitable for freezing therefore not all the eggs retrieved may be frozen. Mature eggs are frozen by first exposing them to a cryo-protective solution and then freezing very rapidly using a process called vitrification.
Each egg is individually frozen and stored. Similar to freezing embryos, once the eggs are frozen they are stable for an indefinite period.
Thawing involves the quick warming of the egg to 37oC and the removal of the cryoprotective solution. After a short period of recovery, the eggs are then suitable for insemination by injecting a single sperm into the egg.
Recent international research has indicated that, on a per thawed oocyte basis, the use of frozen eggs has the potential to give similar results as using freshly collected eggs. Published results suggest a single pregnancy may be produced on average from about 10 -15 oocytes. The number and quality of eggs collected and the overall success rate for the procedure depends on the woman’s age, the reason for the treatment and other factors. There are instances where no eggs may be collected or suitable for freezing despite everyone’s best efforts.