There are two primary reasons why people may wish to consider freezing their eggs.
Firstly, those who are planning to undergo medical treatment that may harm or reduce their egg reserves (e.g. chemotherapy), are offered egg freezing as a means of Medical Fertility Preservation.
Secondly, some are choosing to freeze their eggs in an effort to safeguard themselves for the future, against the age-related decline in fertility that naturally occurs. These cases we refer to as Social or Elective Fertility Preservation.
People are born with all the eggs (oocytes) that they need until menopause. Unlike sperm, which is being constantly produced, eggs start to decline in number from the time of birth. Only about 400 eggs will normally be ovulated from the ovaries in a person’s lifetime.
Maximum fertility occurs in the twenties and by the time a person reaches 35 years old, their fertility has declined by half. This drop in fertility is due to the ageing process, when chromosome abnormalities in the eggs also become increasingly prevalent.
By the time a person is 37 years old the proportion of embryos that are produced with normal chromosomes is thought to be only 50%.
The client will undergo 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 person 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 37 degrees Celsius and the removal of the cryo-protective solution. After a short period of recovery, the eggs are then suitable for insemination by injecting a single sperm into the egg.