On
the morning of oocyte pick-up, a sample of the partner's sperm
is collected by masturbation in a sterile container.
This
sperm has to undergo a special treatment, otherwise it would
be incapable of achieving fertilization in vitro.
In
vivo, sperm is normally transformed under the selective action of
cervical,
uterine and tubal secretions.
These modifications are the separation of spermatozoa from the
seminal
plasma (= the white semi-liquid part of sperm) and the destabilization
of the spermatozoas' cellular membrane.
In vitro,
to mimick natural conditions, the sperm must be "capacitated" in
order to fertilize the eggs.
This "capacitation" is obtained after spontaneous liquefaction
of the sperm, by successive washings (in a medium similar to that
used
for egg culture) and centrifugations aimed at eliminating substances which normally inhibit the fertilizing power of spermatozoa.
(Fig. 6)
At
the end of this procedure a sperm count of the final suspension is
carried out.
The concentration of the medium in which the oocytes are inseminated
is about 100.000 spermatozoa per ml, although only one of them
is expected to penetrate each egg.
When sperm concentration is too low to obtain spontaneous in
vitro
fertilization, it may be necessary to use the technique of
microinjection,
with a micropipette, of one selected spermatozoon into each
egg
(= Intra Cytoplasmic Sperm Injection or ICSO) (Fig. 7)
When
as it sometimes happens, the ejaculate is totally devoid of spermatozoa,
it is possible to collect them through puncture or
biopsy of the testicle or of the epididymis (excretory tract through
which
the sperm normally travels out of the testicle).
Such minor operations are carried out under either local or general
anesthesia, on the day preceding oocyte pick-up.
In this case, the ICSI method is automatically applied for fertilizing
the eggs.
