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Sperm
Invasion Test
When is a sperm invasion
test recommended
The sperm cannot wait to escape from
the acidic environment of the vagina to the more friendly alkaline surroundings
of the cervical mucus. If your mucus is apparently normal in quantity and
"stretchability" and your husband's semen analysis is known to be normal,
one would expect to find an active and progressively motile sperm population
in the mucus at post-coital testing. If after repeated post-coital testing
the sperm are always absent or always dead or only shaking on the spot
instead of progressively moving, this indicates a need for further investigation.
It is obviously important to determine
from you both that intercourse is completely satisfactory and that ejaculation
is taking place within the vagina. Certain lubricants such as K-Y jelly
act as a spermicide, and therefore should not be used by infertile couples.
What is the sperm invasion
test
A special test known as a sperm invasion
test allows the specialist to see for himself whether or not your husband's
sperm can penetrate and survive in your mucus. It also gives him the chance
to perform a microscopic examination of your husband's semen and compare
this with the laboratory report.
How is the test carried
out
You are asked to come to the clinic
at the expected time of ovulation but you must have abstained from intercourse
in the preceding 24 hours. The procedure is then very similar to the post-
coital test in that a mucus sample is withdrawn from the canal of the cervix.
The mucus extracted from the canal
of the cervix is placed onto a glass slide. A drop of semen from
a fresh sample that your husband has produced in the previous hour is then
placed next to it, so that the surfaces of the mucus and semen are in contact
with each other. (The remainder of the semen sample is not wasted but introduced
artificially into the canal of the cervix).
The slide is now examined under a
microscope. The sperm activity is assessed over the next quarter of an
hour. Initially the ability of the sperm to penetrate into the mucus will
be observed. Then the specialist will study whether or not sperm motility
is maintained after mucus penetration.
What are the negative
indications of this test
If sperm penetration does not occur
or if sperm motility is not maintained in the mucus, there is then some
form of antibody interacting between sperm and mucus. Antibodies in the
sperm can inhibit the movement of the sperm. If these antibodies are present
in the mucus, sperm motility will rapidly diminish and eventually stop.
If there are antibodies in the semen sample, the specialist will observe
areas of sperm clumps throughout the sample instead of there only being
freely motile sperm. A clumping or agglutinating antibody is responsible
for sticking the sperm to each other. Tests done on blood samples from
you and your husband can also indicate whether these antibodies are present.
What is the "cross-over
sperm invasion" test
A "cross-over sperm invasion test"
is more specific in that it can help in determining whether the negative
post-coital test is due to some antibody or other factor in your mucus
or in your husband's sperm. While conducting this test, the specialist
will observe the ability of known normal donor sperm to penetrate your
mucus and the ability of your husband's sperm to penetrate and survive
in known normal donor mucus.
How are the investigations
conducted
An ejaculation is made up of several
components. In 90% of patients, the first part of the ejaculate is made
up of most of the sperm and fluid from the prostate gland. The remainder
of the ejaculate is seminal fluid from the seminal vesicles and has a low
sperm content. When the volume of seminal fluid is high, the sperm count
per ml may be very diluted. A semen analysis of the first part of the ejaculate
should reveal a sperm count much higher than for the normal total semen
sample.
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