|
What is cryopreservation?
 Cryopreservation
is a procedure for freezing and storing embryos at a
low temperature. Although scientists have been successfully
freezing sperm for decades, they have not been as successful
with unfertilized eggs; thus far, only fertilized eggs
(embryos) are routinely frozen and thawed.
Water in the embryos is replaced with
a chemical solution (cryoprotectant) that prevents ice
crystals from forming inside the embryos, as this would
destroy them. Embryos are placed in liquid nitrogen
and stored at -196°C. They may be stored this way
for prolonged periods of time. When embryos are thawed,
the cryoprotectant is removed and replaced with water.
About 50 - 65% of good quality embryos will survive
the freeze-thaw process.
Why choose cryopreservation?
Embryo cryopreservation offers
a couple more than one chance to become pregnant from
a single egg retrieval procedure. If there are good
quality embryos remaining after the initial embryo transfer,
they can be frozen and transferred at a later date.
There are additional fees
for freezing and storing embryos.
What are the potential benefits?
- The medication protocol
is simpler as the ovaries do not require stimulation.
- IVF treatment is stressful
and costly. Cryopreservation helps reduce the
inconvenience, discomfort and cost of IVF by
reducing the number of egg retrievals a woman
must undergo, while offering multiple chances
to become pregnant.
|
What are the potential risks?
- The embryo(s) may not survive
the freeze-thaw process (50-65% survival).
- Although freezing offers
couples additional opportunities to become pregnant,
each new attempt may also be another possible
source of frustration and disappointment should
failure occur.
- The existence of cryopreserved
embryos can create pressure for couples to continue
treatment. Although many couples have a strong
desire to try every treatment available to achieve
pregnancy, these feelings may change. At some
point you and your partner may feel you have
done enough and now face the decision of what
to do with stored embryos. This may cause feelings
of guilt about ending treatment and moving on
to pursue other life goals.
- Initially, partners
may be in total agreement about embryo freezing.
However, if problems arise in the relationship,
the question of ownership and disposal of embryos
could become a problem.
|
Who is eligible for cryopreservation?
Everyone involved with IVF treatment
will be offered the option of cryopreservation. Many
couples, however, will not have enough extra embryos
suitable for freezing. The best quality embryos (those
most likely to result in pregnancy) are usually transferred
in the treatment cycle. To be selected for freezing,
embryos must not show any signs of fragmentation (cell
breakdown) or abnormal development. Obviously, not all
embryos will meet these criteria.
How are embryos replaced?
Cryopreserved embryos are usually
returned to the uterus during a menstrual cycle in which
only supplemental estrogen and progesterone are taken.
These hormones enhance the body’s natural cycle
and ensure that the endometrium (lining of the uterus)
is well developed.
About 50-65% of the embryos will
survive
the freeze-thaw process, so we may need to thaw 3 or
more depending on your age in order to obtain
an adequate number
of good quality embryos for transfer. You may be advised
to delay use of your frozen-thawed embryos until after
you have completed a 2nd IVF cycle in order to accumulate
enough embryos before we begin thawing them. It is
recommended
that you wait at least two months following an IVF
cycle
before transferring frozen-thawed embryos. This allows
your body a period of rest before attempting to achieve
pregnancy again.
Back to Top
|
