Embryo
Cryopreservation
A
major goal of an IVF stimulation cycle is to cause
the development of multiple eggs that will be fertilized
to create embryos. These embryos will be cultured
in incubators until ready for transfer.
Sometimes women produce more embryos than can be
safely transferred. Transferring three or more embryos
may greatly increase the risk of high order multiple
births. The number of embryos transferred is different
for specific patients based upon many factors including
age, IVF treatment history, "quality of the
stimulation" and others.
Fortunately,
when there are excess embryos they can by cryopreserved
for future use. The cryopreservation process involves
moving embryos thought different sequential solutions
while gently lowering the temperature. The major
goal is to remove water from the cells, which can
form ice thus damaging the embryos. Eventually,
they are placed in liquid nitrogen for final freezing
and storage. When ready for use they are thawed
using sequential solutions while raising the temperature.
Cryopreserved
embryos are used successfully in IVF cycles; however,
the success rates are somewhat lower than fresh
embryos (this depends upon multiple factors). When
cryopreserved embryos are used it is not necessary
for the female to undergo ovulation induction and
egg retrieval. This greatly reduces the cost of
the IVF cycle. Sometimes, two or more cryopreserved
cycles may result from one IVF stimulation.
Embryos
are routinely cryopreserved and thawed while research
into egg freezing is ongoing. The ability to successfully
freeze eggs will be a major advance allowing women
to save their eggs for future use, store eggs prior
to procedures that may damage their ovaries, such
as cancer chemotherapy, or store eggs for future
IVF cycles. Some centers are reporting limited success
with egg freezing primarily because of the issue
of water in the cell. Remember, water must be removed
so that the delicate egg membrane will not be ruptured.
Ice crystals will destroy the cytoskeletal structure
and cause cell death.
Please
discuss your cryopreservation options with Drs.
Borkowski and Davies.
