Women are increasingly delaying motherhood for a variety of reasons however a woman's fertility declines with age; particularly from their mid to late thirties. This loss of reproductive capacity is largely due to an inevitable decline in egg quality. Consequently there has been a great deal of interest in egg freezing (oocyte cryopreservation) as a means of preserving fertility.
The overall approach is based on assisted reproductive technology (ART) developed to assist couples that cannot conceive naturally. In the case of egg freezing, this is performed soon after the eggs have been collected following ovarian stimulation.
It is important to emphasize that natural conception is best for potentially fertile women as any ART technique can carry an element of risk and overall success rates may be lower than natural conception. All ART involve medical procedures and should only be used when necessary, and after proper consideration of the risks and benefits.
The success of egg freezing is based on the number and quality of the eggs retrieved and that in turn is heavily dependent on the women's age.
Eggs are retrieved once a woman has undergone controlled ovarian hyper-stimulation to increase the number of eggs available for collection. Every woman is different and responds differently to treatment so the number and quality of eggs harvested will vary. Consequently to obtain sufficient eggs to provide a likely chance of pregnancy using frozen eggs, a woman may need to undergo multiple egg retrievals. Even then she may have too few eggs that survive the thawing process or result in healthy embryos and an ongoing pregnancy.
It must be emphasized that ART is not always successful in infertile couples. Similarly the storage of cryopreserved eggs by presumably fertile women does not guarantee a subsequent pregnancy, irrespective of egg number.
Social egg freezing at Monash IVF is restricted to women under 45 years of age. Women considering this treatment aged between 40-45 should be aware that the pregnancy outcomes are significantly lower and there is very little information regarding the viability of this technology for these older eggs.
Monash IVF will not participate in the creation of embryos from cryopreserved eggs after the woman's 53rd birthday. This is based on the socially responsible view that embryos should not be created by women who are past the age of natural menopause.
Reasons for Social Storage
Potential preservation of fertility in the absence of a current male partner or desire for conception and advancing maternal age. The clinical setting varies but includes women in their 30's and 40's who fear that they will not find the right partner until it is biologically too late for natural conception. As in the setting of medical sperm storage, it seems likely (but one cannot be sure) that many women will not ultimately use these eggs.
What does Egg freezing Involve?
Once the eggs have been collected the support cells around the eggs are removed. At this time we can determine whether the eggs are mature. 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, usually by injecting a single sperm into the egg. After fertilization, embryo culture is performed using standard procedures.
How successful is Egg Freezing?
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.