The aim of washing and preparation of the sperm is to separate
sperm from seminal plasma, remove bacteria and other debris and chemicals that
may cause infection and irritation. This improves sperm capacitation (this
helps increase sperm`s ability to penetrate and fertilize an egg).
Sperm can be extracted from seminal plasma by a number of
different methods. The 'Swim up' technique and density gradients are most
commonly used. The swim up technique separates the good motile sperm by
allowing them to 'swim up' into a layer of sterile culture medium. Following
which they are centrifuged and re-suspended in a clean sterile medium (sperm
wash). Density gradient separates normal live sperm from seminal plasma and
other cells and debris by centrifugation on a layer of fluid containing
particles that acts as a filter. The normal sperm become concentrated at the
bottom of the layer and can then be removed and 'washed' by centrifugation and
re-suspended in clean medium.
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There are 2 different procedures which are used to achieve fertilisation
In Vitro Fertilisation (IVF)
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Following egg retrieval, the follicular fluid is immediately
transferred to the adjacent laboratory for identification of eggs, evaluation,
and preparation for insemination. If IVF is being performed, about 3-8 hours
later, between 20000-30000 sperm are mixed with each egg in a drop of specially
prepared culture medium in a labelled dish. This dish is then kept in the
incubator to allow fertilization to occur as they incubate overnight under
controlled laboratory conditions.
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If the sperm and egg are normal, about 60-70% of the eggs
collected will be fertilized. About 5-10% of couples will not achieve
fertilization of any eggs. This could be due to sperm lacking the fertilizing
capacity or poor egg quality. If fertilization does not occur, the eggs have to
be discarded and the remainder of the procedure cancelled. The patient then has
to undergo the ICSI procedure
in the next cycle. To avoid such disappointments, in select cases, we recommend
that half the eggs undergo the IVF procedure and half the eggs the ICSI
procedure.
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Intra-Cytoplasmic Sperm Injection (ICSI)
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This procedure, also known as Sperm Micro Injection, was
developed to treat male factor infertility.There are selected groups of
patients to whom intracytoplasmic sperm injection (ICSI) is recommended.
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Fertilization rates are in the region of 60-70% of the injected
eggs and cleavage rates of about 80% are expected after ICSI. The risk of
complete failure of fertilization is less than 5%. ICSI is generally not
successful when used to treat fertilization failure that is primarily due to
poor egg quality.
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The early stages of ICSI are the same as for standard IVF. The
eggs, after they are aspirated are placed in the incubator for a period of time
usually between 3-6 hours. The eggs are then removed from the incubator and the
cells that surround the egg are stripped off to assess the maturity of the egg,
because ICSI can only be performed on mature eggs.
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Sperm collected from the ejaculate, frozen semen sample or
aspirate from the epididymis
(PESA) or testes
(TESA) is prepared using special cultured medium. Sperm of
virtually any quality and from any level of the male reproductive tract may be
used with the only criterion for use being that the sperm is alive even if it
is not moving (immotile).
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Once the eggs have been selected, a chosen sperm is rendered
immotile, then sucked into the tip of a very fine glass needle and injected
directly into the egg. The egg is held in place by gentle suction on the
opposite side using a holding pipette. This is a very delicate procedure and
involves using a micromanipulator. This process is repeated for each egg. The
elastic nature of the egg membrane means that the tiny hole made by the needle
closes very quickly. About 5% of the injected eggs may be damaged by the
procedure
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