Embryo transfer is a simple procedure that follows
In Vitro Fertilization (IVF) and is often considered the simplest and final step
of the in vitro fertilization process. The objective of embryo transfer is to
facilitate conception following fertilization from the in vitro fertilization procedure.
Embryo transfer is one of the rate-limiting steps in an IVF cycle and plays a
pivotal role in determining IVF success. The day when our in-vitro embryos
return back to us is one of the most exciting moments of an IVF cycle. We
forget the all our struggles; we went through during the whole procedure; since
the invention of IVF, major developments have been made in ovarian stimulation
protocols; the way oocytes are collected; and in the IVF lab; but the embryo
transfer method remains largely unchanged. When different individuals perform
embryo transfer within the same ART programme, the pregnancy rate of each
doctor varies widely. This shows the importance of the embryo transfer
technique and how it determines IVF outcome. It is estimated that 30% of IVF
cycles fail because of shortcomings in this crucial procedure.
There are
many questions, what actually happens during an embryo transfer? Is it an easy
procedure? Will it be painful? Can my embryos fall out of my uterus after the
transfer? Come let us find the answers together
When does
the embryo transfer procedure occur?
Embryos are generally transferred to the woman’s
uterus at the 2-8 cell stage. Embryos may be transferred anytime between Day- 1
through day 6 after the retrieval of the egg, although it is usually between
days 2 -4. Some clinics are now allowing the embryo to reach blastocysts stage
before transferring, which occurs around day 5.
What is an
embryo transfer (ET)?
Transferring one or more embryos into the uterine
cavity of the recipient is called embryo transfer (ET). It is the final and crucial step of an IVF
process. The embryos in the IVF lab are grown usually until day 3 or day 5 in
an incubator in a Petri dish. The qualities of embryos are graded by inspection
under a microscope. The top quality embryo(s) are returned back to the uterus,
where they belong! Even though more than 90% of patients who undergo IVF reach
the embryo transfer stage, only a small percentage of them actually get
pregnant. Unfortunately, not all the embryos which are transferred to the
uterus become deeply desired babies!
What risks
are there with embryo transfer?
There are minimal risks associated with the embryo
transfer procedure. They include the loss of the embryos during transfer or
implanting the embryos in the wrong place such as the fallopian tubes. Although
some women experience mild cramping, the procedure is usually painless.
How is an ET
performed?
During Embryo Transfer, the doctor puts you in the
undignified Lithotomy position in the OR, and inspects your cervix with the
help of a speculum. The sticky cervical mucus is cleared away using a moist
cotton swab carefully. Then the cervix is washed with a sterile fluid. The best
embryos are then loaded into the transfer catheter by the embryologist in the
adjoining IVF lab. He does this under the microscope, and sucks up the embryos
into the catheter by applying negative pressure with the help of a 1 ml
syringe. He brings the loaded catheter
to your doctor, who performs the ET slowly by inserting the catheter into the
uterine cavity through the cervix; and then expelling its contents by gently pushing
the barrel of the syringe. This deposits the embryos into the cavity of your
uterus. This method of transferring embryo(s) to the uterus is called
transcervical embryo transfer. After transferring the embryos, the doctor hands
over the catheter to the embryologist, who then examines it immediately under
the microscope, to see whether there are any embryo(s) retained in the
catheter. If this is the case, the retained embryo(s) are transferred back
again to the recipient. An embryo transfer procedure is normally painless, and
takes only few minutes to perform. You do not need anesthesia for this
procedure. Most embryo transfers are easy but some embryo transfers can be
difficult too; normally your husband is allowed to stay with you during the Embryo
Transfer procedure, in order to hold your hand and provide you with emotional
support, so that you remain stress-free and relaxed.
Are there
any instructions following the embryo transfer procedure?
Once embryos are transferred, there is nothing a
patient can do to influence the outcome of her cycle. Currently, there is no
documented evidence as to whether bed rest or continuing normal activities
following the procedure make a difference in the outcome. Some physicians
encourage the patients to rest for twenty four hours. Others suggest returning
to normal activities as soon as possible. Some patients choose to rest because
they think that by doing so they are improving their chances. Additional rest
also gives them an opportunity to think about the potential baby. Other women
elect to return to normal activities to help them avoid worrying about things that
could go wrong. Together with counsel from the doctor, the state of your body
and mind should help you decide your course of action.
Again, there is no documented evidence showing that
physical activity has any impact upon embryo implantation or conception.
Conception is a natural event that depends primarily upon the genetic quality
of the eggs.
How many
embryos should be transferred?
The number of embryos that should be transferred
during any single IVF cycle is subject to debate. Medical experts and writers
seem to agree that transferring no more than four embryos per IVF cycle will
yield optimal results. Transferring more than four is believed to result in
excess numbers of multiple pregnancies leading to the increase of other
complications; transferring four embryos instead of only one or two increases
the probability of pregnancy but with the risk that all four embryos could
implant.
Are there
any variations in the transcervical embryo transfer method?
Transcervical embryo transfer is performed in two
ways – without ultrasound guidance and with ultrasound guidance.
In the traditional ‘clinical touch’ method, the
catheter is positioned blindly in the desired position, by relying on the clinician’s
tactile senses. In other words the ‘clinical touch’ embryo transfer method
relies on the experience of the person who transfers the embryo; During
ultrasound-guided embryo transfer, the clinician is able to find the
appropriate position for placing the catheter and releasing the embryos using
the ultrasound scan image. During ultrasound-guided embryo transfer, you need
to have a full bladder, so that the uterus can be viewed clearly; It does
create a lot of discomfort for the patient because the embryo transfer
procedure can cause pressure on the already full urinary bladder; the uterus
should not be disturbed during the transfer in order to avoid uterine
contractions - if the uterus contracts, there is a danger of the embryo being
expelled from the cavity.
Is
ultrasound-guided embryo transfer better than ‘clinical touch’ method?
This is a passionately debated topic. There are
studies which reported that ultrasound-guided embryo transfer significantly
enhanced embryo implantation rates; and there are studies which found no
difference if the ET was done by an experienced clinician in the absence of
ultrasound guidance. This is a decision which is best made by your doctor,
based on what works best for him; for junior doctors, an ultrasound guided
transfer seems better, as they learn how to master this procedure.
What are
trial transfers or mock embryo transfer?
Trial transfers or dummy transfers are performed
before the actual embryo transfer. They can be done just before the ET; or
during the ovum pick-up; or prior to the start of the IVF cycle. During a trial
transfer the doctor inserts an empty catheter into the uterine cavity, to find
the easiest passage to the cavity; and to measure the length of the uterus and
the cervical canal. This allows him to measure how deep he has to insert the
catheter, so that he can place the embryo at the appropriate position inside
the uterus, without disturbing the fundus. Most embryo transfers can be
performed easily, but there are some women where the doctor finds it
technically difficult to negotiate the catheter through the cervix. In such a
situation, their cervix has to be dilated to widen the cervical canal, so that
the embryo transfer catheter passes easily through the cervix. There are women
where the doctor needs to use a tenaculum to straighten the uterine axis and
sometimes the uterus is so tilted that the passage of the catheter from the
internal opening of the cervical canal into the uterus is difficult. Sometimes
pulling on the tenaculum alone cannot do the job, especially if the uterus is
acutely angulated in relation to the cervical canal. Then it may be necessary
to curve the catheter, so it conforms to the curve of the uterus. In these
patients, using specially designed catheter sets allows the doctor more freedom
in gently guiding the catheter through the cervix.
What factors
play a role in affecting embryo transfer results?
The embryo transfer should be smooth and trauma-free.
Many studies have shown that the pregnancy rate after embryo transfer is better
if it is performed by an experienced physician, as compared to a newbie.
· Placement of the embryo: Placing the embryo 2 cm
from the uterine fundus (the upper rounded extremity of the uterus, above the
openings of the fallopian tubes) helps in enhancing embryo implantation. This
is the region which is thought to possess maximum implantation capacity.
·
Uterus contraction: When the cervix is handled
roughly or if the catheter touches the uterine fundus, the uterus can contract.
This can expel the embryos from the uterine cavity into the fallopian tubes or
cervical canal, and compromising IVF success.
·
Cervical mucus: Carefully removing the cervical
mucus without causing trauma to the cervix improves IVF outcome. The cervical
mucus can plug the catheter tip , thus preventing the deposition of the embryo
in the uterus. It can also be a source of introducing bacterial contamination
into the otherwise sterile uterine cavity.
·
Catheter choice: Soft catheters have a better
IVF outcome because they avoid trauma to the uterine wall.
·
After the doctor has done the transfer, the
embryologist checks it under the microscope. The presence of blood in the
catheter suggests that the transfer was technically difficult – and this may
reduce pregnancy rates.
·
Trapped embryos: Sometimes the embryos remain trapped with the
catheter, even through the doctor has plunged the barrel of the syringe
completely. When the embryologist identifies the trapped embryos in his petri
dish, he simple reloads them again into a new catheter, and the doctor can then
re-transfer them. This does not seem to affect pregnancy rates.
Why are some
embryo transfers difficult to perform?
Some embryo transfers are difficult to perform
because of the following problems in patients:
1.
Cervical stenosis (narrowing) or anatomical distortion of the cervical
canal and uterus
2.
Acute Utero-Cervical Angulations
If a physician has several years of experience in
doing IVF, then most embryo transfers are like a cakewalk. But in some women,
the embryo transfer can become an arduous adventure because of the difficulty
encountered in traversing the cervix. This is commoner in women of Indian and
African origin, where pelvic inflammatory disease (PID) and cervical infections
are more prevalent. There can also be anatomical distortion of the cervical
canal and uterus because of previous surgery. These conditions might lead to a
traumatic embryo transfer; or the embryo transfer cannot be performed at all.
The presence of an acute curvature between uterus and cervical canal can also
make the embryo transfer hard to perform.
How to avoid
difficult embryo transfers?
Performing mock transfers before the actual embryo
transfer helps in identifying the problem before hand, and can help the doctor
to take precautionary measure. For example patients with cervical stenosis can
undergo a process called cervical dilation to widen the cervical canal. This
might help in the atraumatic passage of the ET catheter into the uterine
cavity. But there are some patients in which transcervical embryo transfer
becomes impossible! In such rare cases, there are other techniques which could
be used to transfer the embryo to the uterus.
What are the
methods which bypass the transcervical route for embryo transfer?
Trans-myometrial
embryo transfer (TET)
In this method, using a special set, two needles
(one inside of the other) are passed through the vagina into the uterus wall,
under ultrasound guidance, until the needle tip reaches the edge of the
endometrial lining. The inner needle is then removed and a thin catheter is
inserted inside the outer needle, which carries the embryo into the cavity. The
embryos are then released in the endometrium. But the success rate with such
embryo transfers are less when compared to transcervical embryo transfers.
Zygote Intra
Fallopian Transfer (ZIFT)
ZIFT stands for zygote intra fallopian transfer.
During ZIFT, cleavage stage embryos are transferred into the fallopian tubes,
instead of the uterus, using laparoscopy. ZIFT is a very good option for women
who cannot have a transcervical embryo transfer, but who have at least one
normal fallopian tube. Since cleavage stage embryos belong to the fallopian
tube and not to the uterus, ZIFT has a higher pregnancy rate than conventional
ET. Most clinics are not able to offer the option of doing a ZIFT, because of
the lack of surgical skills and anesthesia facilities. If your embryo transfers
are difficult, then find a clinic which offers this option!
E-SET
(Elective Single Embryo Transfer)
Elective single embryo transfer (e-SET) is becoming
popular for women who are young and have good ovarian reserve. While
transferring multiple embryos improves the pregnancy rate, it also increases
the risk of multiple gestations. Children who are a result of multiple
pregnancies have an increased risk of health problems, because of the increased
risk of preterm delivery and low birth weight. With the advent of better embryo
selection strategies such as comprehensive chromosome screening (CCS), single
embryo transfer may become the norm in the future.
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