CMV screening during pregnancy

CMV screening during pregnancy is a voluntary, blood-test-based risk assessment that aims to evaluate the risk of a recent cytomegalovirus (CMV) infection in early pregnancy.

 

CMV is one of the most common congenital viral infections. In adults, the infection may be mild or completely unnoticed, but a primary CMV infection shortly before conception or during the first trimester of pregnancy may, in some cases, affect fetal development, especially the fetal brain and hearing.

 

At Fetal Ultrasound Center, we do not see CMV screening as just a blood test. For us, it is part of an integrated fetal medicine care pathway. If a recent primary infection is detected early, the woman can be offered counseling, treatment when indicated, amniotic fluid testing, detailed fetal brain ultrasound, and targeted follow-up during pregnancy.

 

Who is CMV screening suitable for?

 

CMV screening may be considered for any pregnant woman who wishes to know in early pregnancy whether she has previously been exposed to CMV, whether she is susceptible to infection, or whether her blood tests indicate a recent primary infection.

 

The test may be especially relevant for women who have daily contact with young children, because young children may shed CMV for a long time through saliva and urine. However, having a young child at home does not automatically mean that infection has occurred. Screening helps assess the risk more precisely.

 

This is not a national screening program in Estonia, but an informed and voluntary opportunity to assess CMV-related risks in early pregnancy.

 

When should CMV screening be performed?

 

The most appropriate time to perform the CMV blood test is in early pregnancy, around 10–11 weeks

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Fetal Ultrasound Center recommends combining CMV screening with the Fetal Double Test or OSCAR test.

 

If the blood test is performed before the more detailed 12–13-week ultrasound examination, the woman’s CMV serostatus will be known by the time of the visit. This allows early pregnancy risks to be assessed more comprehensively and counseling to be started during the same visit if the screening result is positive or unclear.

 

If the woman has not previously been exposed to CMV, repeat testing may be offered at around 16 weeks of pregnancy.

 

What does CMV screening include?

 

The CMV screening offered at Fetal Ultrasound Center includes three tests:

 

• CMV IgG
• CMV IgM
• CMV IgG avidity

 

CMV IgG shows whether the woman has previously been exposed to CMV.

CMV IgM helps assess for signs of a recent infection.

CMV IgG avidity helps clarify whether the infection may have occurred recently or more likely in the past.

 

These tests are offered together because IgG and IgM alone may sometimes leave the result unclear. IgG avidity helps reduce the risk of false-positive and anxiety-provoking interpretations and makes the result easier for the patient to understand.

 

What does the CMV screening result mean?

 

• If CMV IgG and IgM are negative, this means that the woman is susceptible to CMV. In this case, Fetal Ultrasound Center provides hygiene counseling and offers repeat testing at around 16 weeks of pregnancy.
• If CMV IgG is positive and IgM is negative, this usually indicates previous exposure to CMV and makes a recent primary infection unlikely. However, prior infection does not confer absolute protection against reactivation or against infection with a new viral strain.
• If both CMV IgG and IgM are positive, CMV IgG avidity becomes important for interpreting the result. High avidity is usually a reassuring finding. Low or intermediate avidity may suggest a recent primary infection and requires prompt assessment by fetal medicine.

 

What happens if the result needs further evaluation?

 

If screening suggests a possible recent primary CMV infection, the next steps are discussed with the patient individually.

 

Further management may include counseling about the meaning and risks of CMV infection, discussion of antiviral valaciclovir treatment, monitoring of maternal blood tests, planning amniotic fluid testing, ultrasound examinations to assess fetal growth and development, fetal neurosonography or detailed ultrasound examination of the fetal brain, and, if needed, fetal brain MRI.

 

The need for treatment and further investigations is always decided individually, taking into account the test results, gestational age, international recommendations and the patient’s consent.

 

Amniotic fluid testing when CMV infection is suspected

 

If maternal test results suggest a primary CMV infection in early pregnancy, amniotic fluid testing or amniocentesis may be needed. CMV DNA is detected in amniotic fluid using PCR. The test helps answer an important question: has the virus been transmitted to the fetus?

 

Amniotic fluid testing must be timed correctly. If performed too early, the result may be falsely reassuring. Therefore, according to international recommendations, the test is usually planned after 21 weeks of pregnancy and after a sufficient time interval has passed since the maternal infection.

 

If CMV DNA in the amniotic fluid is negative and the test has been performed at the right time, this provides the family with important reassurance. If CMV DNA in the amniotic fluid is positive, it means that the fetus is infected, but this does not automatically mean a poor prognosis. In this case, the next important step is targeted assessment of the fetal brain, growth, and possible findings suggestive of infection.

 

Detailed ultrasound examination of the fetal brain

 

Assessment of the fetal brain is very important in CMV infection. When needed, Fetal Ultrasound Center offers fetal neurosonography, which is a detailed ultrasound examination of the fetal brain.

 

Neurosonography allows the fetal brain structures to be assessed in more detail than during a routine ultrasound examination. If needed, fetal brain MRI is also recommended.

 

A normal ultrasound examination and neurosonography are reassuring findings for the family, but they do not completely exclude the possibility of later hearing loss. Therefore, if fetal CMV infection is confirmed or suspected, follow-up of the child after birth is also important.

 

What does CMV screening not exclude?

 

It is important to understand that CMV screening does not provide a complete guarantee that no CMV-related risk will arise during pregnancy.

 

Standard CMV serological screening is not intended to reliably detect CMV reactivation or reinfection with a new viral strain in women with prior CMV immunity. If a woman who is CMV IgG positive develops ultrasound findings suggestive of infection during pregnancy, the situation is assessed individually regardless of the initial screening result.

 

CMV screening is not a test aimed at termination of pregnancy. Early knowledge instead provides an opportunity to act at the right time: to offer counseling, consider treatment, plan diagnostics, and assess fetal brain development systematically.

 

How can CMV risk be reduced during pregnancy?

 

CMV spreads through body fluids, especially saliva and urine. For pregnant women, one important source of infection is often a young child.

 

 

The risk can be reduced by washing hands after changing nappies and after contact with a child’s saliva. It is also recommended not to share the same spoon, cup or drinking bottle with a young child, not to put a child’s pacifier into your own mouth, to avoid kissing a young child on the lips, and not to share a toothbrush with the child.

 

These simple hygiene measures do not provide complete protection, but they may reduce the risk of primary CMV infection during pregnancy.

 

If the screening result is positive or unclear, the patient is not left with only a laboratory result. At Fetal Ultrasound Center, the results are discussed with the patient, and, when needed, a further management and follow-up plan is prepared based on the test results and gestational age.