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Cytomegalovirus (CMV) and Pregnancy
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Cytomegalovirus infects many adults during their lifetime. It usually manifests
as inflammation of the upper respiratory tract, sometimes involving severe tonsillar
pain, fever, fatigue, rashes, etc. In most cases, however, the illness is so mild
as not to be noticeable. The virus does not cause damage to adults. After resolution
of the illness, antibodies that immunize us against recurrent infection appear.
How are the antibodies expressed in the blood? The long-term antibodies remaining
in the blood are of IgG type, whereas those appearing immediately at the time of
infection and subsiding within a few months are known as IgM. There is an avidity
index that checks the percentage of "chronic" IgG antibodies. Usually, an avidity
index of greater than 45% indicates that infection occurred more than 3 months before
the blood test. In the case of a "non-fresh" infection, a repeat blood sample taken
two weeks later will not show a significant change in either IgG or IgM (the previous
and repeated sample must be tested together in the same batch). The virus is excreted
in the urine during the acute infection - infrequently, it continues to be excreted
for a significant time, and during this time the mother can infect her fetus.
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Even though the virus does not cause damage to adults, if the mother has had a CMV
infection during pregnancy, the virus may pass through the placenta and infect the
fetus.
Fetal infection during pregnancy can cause severe problems, especially if it occurred
during the early stages of the pregnancy.
The virus usually affects brain tissue and causes disruption of the development
of the brain, deafness, convulsions
after birth, delayed growth, etc.
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What should be done in cases of suspected maternal infection during pregnancy? It
is recommended that amniocentesis be performed 8 weeks after the infection, but
only after the 20th week. A PCR test is performed (Polymerase Chain Reaction - replication
of the genetic material of the virus which allows very small quantities to be analyzed),
and a culture is grown from the amniotic fluid by growing the virus on a special
medium for a month. If the virus is not demonstrated in the amniotic fluid, the
risk that the fetus was infected with CMV is very low. Monitoring the growth in
the fetus's head circumference and the size of the femoral head is also important.
Fetuses with CMV infection will only demonstrate a slower growth rate based on these
parameters in ultrasound scans carried out in the third trimester (after week 24).
Even if there is no evidence of a fresh CMV infection in the pregnancy, the growth
of the head circumference or growth rate of the femoral head can be monitored by
ultrasound.
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