The ultimate goal of in vitro fertilization
( IVF ) is a healthy single intrauterine pregnancy. IVF involves stimulation
of egg development through the use of medications ( gonadotropins ). After
retrieval of the eggs and fertilization, embryos are produced that
are capable of continued normal development leading to a successful pregnancy.
The challenge for the in vitro fertilization team is choosing embryos
most likely to result in pregnancy.
A blastocyst is an embryo that has developed for five
days after fertilization and has divided into two different cell types.
A healthy blastocyst should hatch from its "shell" ( zona pellucida
) by the end of six days, and within 24 hours after hatching, should begin
to implant within the lining of the uterus. Recent studies have demonstrated
that embryos that do not survive to the blastocyst stage have a high incidence
of abnormal chromosome numbers.
Thus, culturing embryos to the blastocyst stage may
significantly decrease the number of abnormal embryos. The transfer of
high - grade blastocysts has resulted in implantation rates between 30%
- 40% in selected populations. With the transfer of only two blastocyst
embryos, pregnancy rates as high as 50% - 60% per cycle have resulted.
These high implantation and pregnancy rates are due in large part to selection
of those embryos that have the highest chances of producing a pregnancy.
Most of our embryo transfers are performed on day two
or three. However, recently, improvement in embryo culture conditions
have allowed sustained embryo development to the blastocyst stage ( the
stage at which the embryo naturally arrives to the uterine cavity and
implantation occurs ). Preliminary studies with the new culture media
in good responder patients have shown that approximately 40% - 50% of
the fertilized eggs reach the blastocyst stage. This allows for better
selection of the embryos to be transferred and to limit the number of
embryos transferred to two in order to eliminate the risk of a triplet
pregnancy or higher. The transfer will usually occur five to six days
after egg retrieval.
The pregnancy rate does not seem to be significantly
different from day three transfers, but the implantation rate ( number
of gestational sacs by ultrasound / number of embryos transferred ) is
higher. Excess blastocysts will be frozen at that
stage. Candidates for blastocyst transfer are patients with at least
six embryos and under the age of 40. However, as in the other areas of
IVF treatment, the day of transfer and number of embryos to be transferred
is discussed with the patient.
There are some unresolved issues currently regarding
blastocyst transfer; therefore, the procedure is not appropriate for every
couple. In a small percentage of patients, none of the embryos progress
to the blastocyst stage; they gradually degenerate resulting in a loss
of all embryos. Thus, there must be a sufficient number of embryos available
as some are lost in the culturing process.
The possible disadvantages of blastocyst transfer include
a longer time interval between retrieval and transfer, fewer embryos that
can be frozen, and the potential for lack of transfer due to degeneration
and arrest of the embryos prior to the blastocyst stage. The experience
with blastocyst freezing also is growing at the present time.
We at the Jones Institute are optimizing blastocyst
culture and transfer. The decision to perform blastocyst culture and transfer
is based on several factors including patient age, egg age in cases of
donor egg, the number of eggs retrieved, previous IVF success, and perhaps
most importantly, the embryo grade and cell count on day three of culture.
Blastocyst culture and transfer may have significant
advantages for younger patients, egg recipients who receive eggs from
younger donors, high responders ( many eggs retrieved ), or patients with
previous IVF success. We encourage you to discuss the possibility of blastocyst
transfer with your infertility
physician.
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Phone
800-515-6637 or 757-446-7100