Diagnosing maternal infection with CMV during pregnancy

The protocol of the Ministry of Health in Israel, like most Western countries, is not to perform routine tests for CMV virus detection in blood tests in pregnant women, and this should be particularly avoided after the first trimester.

Despite this, many gynecologists refer to the blood test detecting CMV virus antibodies as part of the blood tests that are performed in the first weeks of the pregnancy.

Reading the blood tests (serology tests)

Antibodies are the primary component of the immune system.
The CMV virus blood tests check three parameters, including two types of antibodies:
IGG antibodies and IGM antibodies:
IGG antibodies provide the body with long-term protection after infection, and a positive result for these antibodies in the blood shows that the tested woman was infected with the virus in the past.
IGM antibodies are the antibodies that appear first following primary infection.
In addition, a value called AVIDITY can be tested, which tests the efficiancy of the IGG antibodies, and can therefore help date the estimated time of infection.
The HMOs use different lab kits, and therefore different labs have a different scale for this parameter. Nevertheless, according to all value scales, a high AVIDITY value will be evidence of infection that occurred more than three months before the blood test was performed.

 

Possible results:

 

Positive IGG and negative IGM – the woman was infected in the past and is currently not ill. Even if the virus in her body is activated, or if she contracts another strain of the virus, the risk for fetal infection and illness is low, so most doctors will recommend not to conduct any special follow-up. See non-primary infection in the Q&A tab.

 

Positive IGG and positive IGM – the woman was probably infected recently. Why “probably” and not certainly? Since the IGM value can be positive for several months, and even years, after the primary infection. In addition, there may be a non-specific reaction from another virus other than CMV, which can result in a false positive of IGM value.

 

Negative IGG and negative IGM – the woman has never contracted the CMV virus. In this case, if she is pregnant, or plans a pregnancy in the near future, she is at risk for primary infection during pregnancy and has to take precautions.

In such a case, the Ministry of Health guidelines are as follows:

  1. Providing an explanation on the risk for primary infection with the CMV virus and instruction on how to reduce the risk for infection with the virus.
  2. Informing women tending to infants (mothers, kindergarten teachers and caretakers in nurseries and kindergartens) of the increased risk for exposure to the CMV virus due to the close contact with infants, and also providing an explanation on the importance of close adherence with the instructions for the prevention of infection. See more details under the tab Q&A.
  3. Repeating the serology test for CMV virus IGG and IGM antibodies every 4-6 weeks until gestational week 30.

 

Negative IGG and positive IGM – this result can represent two conditions:

  1. New CMV virus infection, so that IGG antibodies level has not had time yet to rise
    (In this case, another blood test needs to be performed 2-4 weeks later).
  1. A false positive, resulting from the sensitivity of the IGM parameters, which can erroneously react to infection with other infectious agent other than the CMV virus, and which are not relevant for the fetus during pregnancy.

Additional results of blood tests:

Borderline IGM – can indicate that an active disease is starting or ending. In this case, the additional data need to be examined, in order to determine the stage.

VIDAS or Additional Assay – a more specific method for measuring IGM and IGG antibodies, which makes it possible to obtain more accurate data.

The range of options and the fact that in Israel, many labs carry out the serology tests for the CMV virus, stress how important it is that the reading of these lab test results is made by a person with expertise on the subject, in order to avoid overdiagnosis or underdiagnosis

You can find a list of CMV specialists and CMV clinics under the tab Important Telephone Numbers. 

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