Pregnancy starts with
the fertilization of an egg with a sperm to form an embryo, which implants
itself to the uterine lining. Therefore, it would not be wrong to say that the
embryo is the building block of pregnancy, whether natural or assisted. In
context of the commonly used artificial reproductive technique IVF, embryo
culture implies the formation of zygote and its growth into a embryo.
IVF starts with egg
retrieval from the ovaries of the patient and these eggs are fertilized with
sperms to form a zygote. The zygote is then allowed to grow by placing it in an
artificial medium and under favorable conditions. The growth of zygote into
embryo, or embryo culture, takes 2 to 5 days to be completed. The embryo is
then placed into the uterus for the pregnancy to continue in the normal manner.
The success of IVF
greatly depends upon the conditions made available for embryo culture, because
it is actually a healthy embryo which generates a healthy pregnancy. Therefore,
IVF patients need to ensure that the procedure of embryo culture should be
carried out to perfection and the embryos remain safe while they are in the
lab, before being transferred to the uterus.
Understanding
Embryo Culture- The Procedure
Embryo culture is one
of the most vital and delicate steps involved in IVF as it requires a great
degree of skill and expertise to be completed successfully. A process of 2 to 5
days, it is carried out in a series of steps.
Fertilization:
The Formation of Zygote
The procedure begins as
soon as the follicular fluid is aspirated from the ovaries of the patient. It
is carried to the lab, where the embryologist makes its microscopic examination
for identifying the eggs present in it. A special medium is used to wash away
the toxins as well as impurities around the egg and the surrounding cells. From
here, they are taken into carbon dioxide filled incubators, where they are
placed in separate dishes. The eggs are then allowed to mature for
fertilization, a process taking 2-6 hours in all.
Once the eggs are
mature for fertilization, they are made to combine with the male sperms, which
too have been washed. This process is carried out in a dish which contains a
culture medium, a fluid comprising of salt, proteins and antibiotics. This
medium, known as Human Tubal Fluid (HTF) medium, is specially formulated to
facilitate the cell division and fulfill the metabolic needs of the growing
embryo. Once set for fertilization, the dish makes it way back into the
incubator.
Monitoring
of the Embryos
Embryo culture is not
just about synthesis of the embryos in the lab, but they also have to be
monitored carefully to ensure their quality. The embryo requires a controlled
environment to grow and flourish into a healthy one and has to be monitored
carefully by a qualified embryologist. The next growth milestone is achieved by
the embryo after a period of 18 hours. The stage reached is called the
pronuclei stage and it is characterized by the formation of two clear bubbles
in the embryo. This is the time where the embryologist discards the embryos
without the pronunlei.
The embryos are given
another 24 hours to develop and from here on, monitoring is done for cell
division. This is the time when the embryos would divide into two to four cells
(cleavage stage which comes after 2-4 days), a stage considered favorable for
the implant by some clinics. On the other hand, some clinics transfer the embryos
later, when they reach the blastocyst stage (after 5 days). The decision is
based on factors like the health conditions of the patients and the protocol
followed by the clinic.
What
is the right time duration of embryo culture?
Another factor which is
used to determine the success rate of embryo culture and the safety of the
embryos in the lab is the time duration of the procedure. Basically, it can
vary from patient to patient, depending upon the reproductive history of both
the partners. Accordingly, there are three options made available to the
patients to choose amongst.
A two day embryo
culture is recommended for the couples which have low number of embryos for
implantation or they are not showing reasonable development. At this stage of
transfer, the cultured embryos are at a two or four cell stage.
In cases where
increased monitoring is needed, three day embryo culture is the feasible
option. This is the time when the embryo has reached a six to eight cell stage.
The chances of viability of the embryo are better at this stage because they
have been checked for cleavage and gene activation.
Patients with history
of recurrent miscarriages or failed IVF cycles are suggested to opt for
blastocyst stage embryo transfer, which is reached after five days of embryo
culture. Here, the embryo (blastocyst) has divided into 12 to 16 cells, giving
them better chances to implant and become a successful pregnancy.
Are
the embryos being cultured getting the right environment in the lab?
The growth of embryos
in the lab is determined by the environment being made available to them.
Primarily, two parameters are to be considered in this regard.
·
Culture
medium refers to the medium in which the embryos are placed
during the stage. This medium is specially designed stage-wise, the first one
during the stage of initial embryo development/cleavage medium (up to day 3)
and the second one in the later development stage/blastocyst medium (from day 3
to day 5). Embryos cultured with normal fertilization are placed in the former
while those allowed to reach blastocyst stage or to be taken further for
cryopreservation would have to be subjected to the latter
·
Temperature
also
has to be carefully maintained and monitored to ensure the success of embryo culture
process. The temperature inside the incubator has to correspond with that
available to the embryo inside the Fallopian tube, which is nearly 37 degree
Celsius.
The patient can ensure
the safety of their embryos in the IVF lab by checking out whether these
factors are being looked after well enough. The success rate of embryo culture
can be maximized this way, but the fact is that one should be realistic in
their expectations as problems may still crop up despite best care and
precautions.
Gaudium
IVF is a leading specialist clinic, trusted for providing world class
facilities and lab conditions for its patients. To get these facilities along
with the expert advice from the renowned fertility specialist Dr Manika Khanna,
get in touch today.
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