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What is egg freezing?
For many years it has been possible for couples undergoing
IVF treatment to have embryos frozen and stored for future use. It has taken
longer to develop methods for freezing eggs, as they are more vulnerable to
the damage that can take place when cells are cooled. Techniques have now
been developed that enable eggs to survive freezing and thawing, to be
fertilized, develop into embryos, and give rise to normal pregnancies. Eggs
are treated using a solution containing sugar and antifreeze, and are cooled
very slowly, under computer control. They are then transferred to storage
tanks containing liquid nitrogen.
Who needs egg freezing?
Egg freezing may be used in any situation where eggs are
collected from a woman’s ovaries and there are no sperm available to
fertilise them and create embryos. Women who have cancer and require
treatment that may harm their ovaries, damage their future fertility. If
they do not have partner, and are therefore unable to store embryos, it is
possible to freeze eggs so that their future fertility may be preserved (if
only in a limited way). As it is necessary to use drugs to stimulate the
ovaries in order that enough eggs develop for freezing to be carried out,
women with certain types of cancer will not be able to undergo freezing,
either because they need to start treatment immediately, or because their
disease is sensitive to the drugs that are used in ovarian stimulation (e.g.
oestrogen sensitive tumours.
Women who are suffering from a condition that may lead to
premature ovarian failure, and, as a result, infertility, may also consider
egg freezing.
Egg freezing is also available to women who are unable to
start a family at present, but who are concerned about their future
fertility.
Finally, egg freezing may be used as an emergency procedure
for couples undergoing IVF, if for any reason, the male partner is unable to
provide sperm at the time of treatment.
What does egg freezing involve?
In order to collect enough eggs to freeze, women must
undergo drug treatment to stimulate their ovaries, in the same way as women
undergoing IVF treatment. This takes two to five weeks. The eggs are
collected, usually under general anaesthetic, by sucking fluid out of the
follicles that develop on the ovaries, which contains the eggs. Only eggs
that are mature, i.e. are ready to be fertilized, can be frozen, and the
embryologist will check the maturity of each egg prior to freezing.
When the eggs are required for treatment, they are thawed
and fertilised using a technique known as intracytoplasmic sperm injection
or ICSI. This involves injecting a single sperm into each egg. This results
in a much better fertilization rate with frozen eggs than conventional IVF.
How
successful is oocyte freezing?
Egg freezing is new technique and it takes time to
accumulate results, as eggs may be stored for several years before they are
used. Over a hundred babies have now been born world wide, with no reports
of any abnormality, but this is a very small number, and we cannot yet draw
any definite conclusions about the safety of the technique.
A survey of the literature has shown the survival rate for
good quality egg about 60%. The fertilisation rate for ICSI using frozen
eggs (that have survived) ranges from 56% - 64%. Thus cryopreservation of
eggs is still considered a low efficiency technique.
What are the risks of oocyte freezing?
Earlier experiments on egg freezing suggested that cooling
eggs resulted in damage to the arrangement of chromosomes, which prevented
fertilization and normal development. Current techniques appear to have
overcome this problem, and there have been no reports of abnormalities in
babies born from frozen-thawed eggs. However, the numbers are still low, so
we cannot yet draw any definite conclusions. Nevertheless, the data so far
does not suggest any cause for concern.
For
further information, read our treatment information sheet:
EGG FREEZING
(You will need to have
Adobe Acrobat Reader, which can be downloaded free from
www.adobe.com)
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