Egg and ovarian tissue freezing has the potential to help women with cancer, as chemotherapy and radiation treatment can often have a harmful effect on fertility, rendering many of these women menopausal.
Women who are at risk of early menopause, have a genetic disorder that could limit fertility or wish to have children at a later date can also have eggs or ovarian tissue collected and stored.
Some patients taking part in an IVF program have moral or ethical beliefs against freezing supernumerary or excess embryos and may prefer to store unfertilised eggs instead. The ability to cryopreserve eggs before fertilisation means that if they are surplus to requirements in the future, their disposal would not raise some of the moral or ethical dilemmas that the discarding of embryos may.
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Our ability to freeze any cell depends on many factors, but most significantly on how much water it contains. Because water expands in volume as it turns to ice, cells must be dehydrated before freezing to prevent them from rupturing. The addition of a cryoprotectant, which does not expand upon freezing, can greatly reduce the risk of cell rupture.
Scientists have been freezing and thawing sperm with success for more than 100 years. In many ways, sperm are ideal for freezing as they exist as individual cells, are the smallest human cells and contain very little water. It is thought that sperm can be stored perhaps indefinitely after being added to a solution of cryoprotectant and then frozen to minus 196C.
In contrast to the sperm, the egg is the largest human cell and contains much more water. The egg is also much more sensitive and is highly intolerant of the chemical and physical stresses that may be created during freezing and thawing. Further, the availability of eggs is much more limited. When an egg is ovulated, or retrieved from the ovary during an IVF cycle, ideally it is ready to be fertilised by a single sperm. In anticipation of fertilisation, the egg prepares to discard half of its DNA in a process known as meiosis. Any changes in the physical or chemical environment around the egg can disrupt meiosis, leading to an egg with too much or too little DNA. So even after we overcome the hurdles of sensitivity and cell water content, these other obstacles to successfully freezing and thawing eggs remain.
City Fertility Centre uses the “vitrification” method for freezing eggs. This is the process whereby the solution containing the egg is cooled so rapidly that the water molecules do not have time to form damaging ice crystals and instantly solidify into a glass-like structure. The concept is based upon the idea that if the cell is dehydrated to a certain degree and then cooled fast enough, everything will “freeze” in place and damage will not have time to occur.
Compared with the traditional slow-freezing methods, which are still the preferred option for many IVF laboratories today, vitrification at City Fertility Centre is delivering enhanced survival of preserved eggs and fertilisation rates nearing those of freshly retrieved ones. This is encouraging news for those wanting to freeze eggs for medical or fertility preservation reasons.
For more information on vitrification, please refer to the Vitrification Fact Sheet.
The alternative approach of freezing an abundance of immature oocytes contained within ovarian tissue has been the subject of intensive research within the international IVF community over the past five to 10 years. For this process to be successful, the oocytes contained within the immature (primordial) follicles had to be able to survive freezing and go on to mature to a stage where they can be fertilised normally.
In the late 1990s the IVF community, having established optimal methods for ensuring that the follicles and immature oocytes in ovarian tissue could withstand storage at very low temperatures, began searching for ways to prove that these follicles and oocytes could undergo normal development to maturity. We now know this is possible. Using a technique whereby small samples of previously frozen tissue are grafted into a special type of laboratory mouse that cannot reject the graft (xenografting), scientists have been able to show that multiple mature follicles and oocytes are able to develop within the tissue frozen by this method. Importantly, we have also been able to show that this technique is reproducibly true for small samples of tissue frozen from a wide range of patients.
A number of groups worldwide have now started to take the first tentative steps towards applying this technology by grafting frozen/thawed tissue back to patients. Early reports of evidence of transient ovarian function after grafting provided only limited encouragement but more recently there have been further indications that ovarian function, and even fertility, may be reinstated through this method.
The potential disadvantage of using ovarian tissue harvested due to cancer is the theoretical possibility that these cancer cells will still be present in the ovarian tissue and may re-establish within the body once grafted.
Similar to the early days of IVF, this technology is still in its infancy but the potential benefits to a particularly vulnerable group of young women are enormous. Progress in assisting the ability to preserve future fertility will potentially have major implications for this group of women, both medically and socially.
City Fertility Centre follows guidelines recommended by the National Health and Medical Research Council (NHMRC 2004) regarding egg or ovarian tissue storage. The maximum time that eggs or ovarian tissue can be kept in storage at City Fertility Centre is five years; however, couples do have an option to renew consent to store for a further five years. If the maximum 10-year period passes and the stored material has not been used or donated to another couple, and no alternative arrangements have been made by the owners (and the owners remain untraceable), disposal will be arranged.
If your cryopreserved material is reaching the 10-year storage limit and you would like an extension, you must apply in writing to the scientific director of City Fertility Centre.
If you decide to dispose of your cryopreserved eggs or ovarian tissue at City Fertility Centre, please contact the nurse coordinators to discuss the options. You will need to sign consent forms before disposal of the material. We ask all patients with stored cryopreserved eggs or ovarian tissue to keep City Fertility informed of their current contact details. A six-monthly storage fee applies. Storage fees will cease if you decide to dispose of your material.
The following options are available to you if you decide to no longer keep your eggs or ovarian tissue cryopreserved:
Whichever option you choose, signed consent forms are required before release of your material. Please contact the nurse coordinators to discuss these alternatives. At this point you will no longer be charged storage fees.
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