What are freezed embryos? Should
you freeze yours when opting for an IVF?
Since most IVF programmes superovulate patients to grow many eggs, there are often many embryos. Since the risk
of multiple pregnancies increases with the number of embryos transferred
(and in fact the law in the UK prohibits the transfer of more than 3 embryos
to reduce this risk), many patients are left with "spare" or supernumerary
embryos. These can be discarded; or used for research.
It is now also possible to freeze
these embryos and store them in liquid nitrogen. These stored embryos can
then be used later for the same patient - so that she can have another embryo transfer cycle done without having to go through superovulation
and egg collection all over again. Moreover, since this embryo transfer
is done in a "natural" cycle (when she is not taking any hormone injections)
some doctors believe the receptivity of the uterus to the embryos is better.
For women with irregular menstrual
cycles, frozen embryo transfer can also be done in a "simulated natural
cycle", in which the endometrium is primed to maximize its receptivity
to the embryos by using exogenous estrogens and progesterone. Since pregnancy
rates with good-quality frozen-thawed embryos are as good as with fresh
embryos, we encourage all our patients to freeze and store their supernumerary
embryos, rather than discard them. Freezing is very cost-effective, since
transferring frozen-thawed embryos is much less expensive than starting
a new cycle, so that it serves as a useful "insurance policy" in case pregnancy
does not occur.
However, since it is worthwhile freezing
only good quality embryos, the option of freezing is a "bonus" which is
available to only about 30% of all IVF patients. About half of all embryos
frozen survive the freezing thaw process. It is reassuring to know that
the risk of defects is not increased as a result of freezing. These frozen
embryos can be stored for as long as is needed - even for many years. When
they are in liquid nitrogen, at a temperature of -196º C, they are
in a state of suspended animation, and all metabolic activity at this low
temperature stops, so that a frozen embryo is like Sleeping Beauty!
Once stored, embryos can be used
by the couple during a later treatment cycle, donated to another couple
or removed from storage. These options should only be undertaken after
While we still cannot freeze unfertilised
human oocytes efficiently, a new technique called vitrification (which
uses ultra-rapid cooling together with an increased concentration of cryoprotectants)
may allow us to offer this option to our patients, in the future, allowing
the facility of egg storage and egg banking.
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- The Indiaparenting Team