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Blastocyst Transfer
The blastocyst culture and transfer procedure for in vitro fertilization
facilitates selection of the best quality embryos for transfer to the uterus
of the mother. The concept of embryo quality is a very important one for
couples experiencing infertility. With blastocyst embryo transfer, we can
transfer fewer embryos - reducing risks for multiple pregnancy - while
keeping overall pregnancy rates high.
A blastocyst is an embryo that has developed for five to seven days after
fertilization. At this point the embryo has two different cell types and a
central cavity. It has just started to differentiate. The surface cells,
called the trophectoderm, will become the placenta, and the inner cells,
called the inner cell mass, will become the fetus. A healthy blastocyst
should begin hatching from its outer shell, called the zona pellucida by the
end of the sixth day. Within about 24 hours after hatching, it should begin
to implant into the lining of the mother's uterus.
The ultimate goal of in vitro fertilization (IVF) and embryo culture is to
provide high quality embryos which are capable of continued normal development
and result in live births. However, under standard IVF culture conditions,
only about 20-40% of human embryos will progress to the blastocyst stage after
5 days of culture. This low rate of embryo development is the result of a
less than optimal culture environment for the embryos. For this reason,
embryos have usually been transferred into the uterus after only 2-3 days of
culture.
One problem with this is that 2 to 3-day-old embryos are normally found in
the fallopian tubes, not in the uterus. The embryo first moves into the
uterus at about 80 hours after ovulation. The implantation process begins
about 3 days later - after blastocyst formation and hatching have occurred.
Therefore, if in vitro culture conditions could be improved so that
blastocysts formed at a higher rate, then embryos could be placed into the
uterus at the blastocyst stage - at a more "natural" time, and shortly before
implantation should occur.
Transferring blastocysts following IVF also provides another benefit -
reduction of the possibility of multiple pregnancy. Some 2 or 3-day-old
embryos do not have the capacity to become high quality blastocysts and a
viable pregnancy. However, on day two or three of culture we do not have
reliable methods to determine which embryos will be viable long-term. By
culturing embryos to the blastocyst stage we have more opportunity to choose
the most competent ones for transfer. We can then transfer fewer embryos and
obtain high pregnancy rates with less risk for high order (triplets or
higher) multiple pregnancy.
In the past, it was very difficult to get good numbers of high quality
blastocysts with in vitro culture systems - unless "feeder" cells were
utilized - coculture. However, new culture media have recently become
available that yield much higher blastocyst formation rates. This makes
blastocyst transfer a viable option for some couples with infertility.
Pregnancy rates with blastocyst transfer
Pregnancy rates with blastocyst transfer are potentially very "tricky".
Because almost all clinics are selective in choosing patients that will be
eligible for this procedure, we should expect that pregnancy rates would be
higher as compared to the rates seen in "unselected" patients.
This does not mean that having a blastocyst transfer increases a couples
chance for pregnancy. It means that if we select patients for blastocyst
transfer that are younger and have more embryos of better quality - we should
have higher pregnancy rates - because we already know that those patients
are more likely to have success - whether we transfer on day 3 or day 5.
The real potential of blastocyst transfer is to reduce the risk of multiple
pregnancy by transferring fewer embryos of higher quality. We have had a
very low percentage of triplet (or higher order) pregnancies from blastocyst
transfer. Thus far the rate of triplets has been less than 3% at our center.
These triplets have been the result of "identical twin" splitting of an
embryo - 2 transferred and 3 implanted. We have never seen quadruplets or
higher with a blastocyst transfer.
Having said all of that, here are the pregnancy rates for blastocyst transfer
cases at our IVF clinic.
OUR PREGNANCY RATES FOR BLASTOCYST TRANSFER
Advanced Fertility Center of Chicago
Blastocyst transfer cases performed in our clinic between 1998 and December
31, 2002
Under age 35, using own eggs
Per egg retrieval
Per embryo transfer
Clinical pregnancies
70 of 109
64.2%
70 of 109
64.2%
Age 35-39, using own eggs
Per egg retrieval
Per embryo transfer
Clinical pregnancies
19 of 39
48.7%
19 of 39
48.7%
Clinical pregnancies are those with a pregnancy sac seen in the uterus on
ultrasound
Some clinical pregnancies will later miscarry
Blastocyst transfer cases performed in our clinic between 1998 and December
31, 2002
Only couples without any previous IVF failures
Under age 35, own eggs
No previous IVF failures
Per egg retrieval
Per embryo transfer
Clinical pregnancies
56 of 77
72.7%
56 of 77
72.7%
These pregnancy rates are for women under age 35 that had blastocyst transfer
in our clinic and never failed IVF previously. The pregnancy rate is higher
here because couples with previous failure(s) are in a somewhat lower yield
situation (on the average).
A comparison of clinic success rates may not be meaningful because patient
medical characteristics and treatment approaches vary from clinic to clinic
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