A positive diagnosis can be confusing and stressful. This section aims to explain how doctors diagnose CMV during pregnancy or after birth, what this means and where you can go for further support.

Diagnosis and Management in Pregnancy

Sometimes there will be a concern about a pregnant mother being unwell during pregnancy, or concerns about the baby’s development leading to mother being tested for CMV infection.

How do I know if I have CMV?

Most healthy children and adults infected with CMV have no symptoms and may not even know that they  have been infected. Others may develop a mild illness; symptoms may include fever, sore throat, rash and fatigue.

Other symptoms, such as swollen glands, liver or spleen, may sometimes be present. However, these can be symptoms of a wide range of conditions, not just CMV.  Always talk to your doctor or midwife if you have concerns.

A blood test can tell if you have an active CMV infection or have had a previous infection.  Doctors can diagnose a maternal primary CMV infection (catching CMV for the first time) by testing for Immunoglobin M (IgM) and Immunoglobin G (IgG) antibodies and performing an “avidity” test, which checks how tightly the IgG binds to CMV.  By analysing levels of these antibodies and the avidity test, an estimate of the timing of CMV infection can be made.  These results will be interpreted by a virologist, as they are not always straight-forward.  Sometimes your midwife or doctor may ask you to have further blood tests done a few weeks later to help interpret the results of your tests.  

The timing of CMV infection is associated with the risk that the baby will be affected by congenital CMV.  If CMV infection is contracted in the first trimester, the risk of long-term problems is estimated at less than 1 in 100 and the risk in the third trimester is negligible.  Whilst the risks in the later stages of pregnancy are thought to be very low, the studies that report these findings have only followed up infants for the first few years of life, and longer-term studies are yet to report.

As the risks are highest around conception and early pregnancy, it is particularly important that women planning pregnancy or in the early stages of pregnancy take particular care to reduce the risks of catching CMV.

Even if you have had CMV before, it is still possible to catch a different strain. It is therefore important for all pregnant women, and those planning a pregnancy, to follow simple hygiene precautions even if they have had CMV before – nobody is ‘immune’.

Why isn’t CMV routinely screened for in pregnancy in the UK?

The UK National Screening Committee has recommended against routine screening for CMV in pregnancy. This is because most babies with CMV develop normally.  Also screening would only detect cases of primary infection and tests available at present are not able to diagnose secondary infection (infection with a new strain or reactivation of the original strain of CMV).

I am pregnant and have been diagnosed with CMV: what does this mean for me and my baby?

Being  diagnosed  with  CMV infection when you are pregnant can be very stressful. However, it does not necessarily  mean  that your baby has the virus, or that they will have problems associated with CMV. Of all the women who catch CMV for the first time during pregnancy, two-thirds of women will NOT  pass it to their unborn baby and most babies who do have CMV remain well.

However, all women who are diagnosed with CMV infection in pregnancy should have additional scans so that any signs of CMV in the fetus can be found. These may include small for gestational age growth, microcephaly (small head) or altered signals in the brain or bowel.  You may be offered an amniocentesis (taking some water from the sac around the baby) to see if your baby has been infected.  It is recommended that an amniocentesis should take place at least 6 weeks after maternal infection, and after 20 weeks of baby’s gestation. 

It is important to remember that even if the virus has been passed on to your unborn baby, around 4 out of 5 babies born with CMV don’t have any health problems at birth.

Doctor examining baby with stethoscope

Symptoms and Diagnosis in Babies

Symptoms of congenital CMV in babies are very wide ranging.  Most babies born with congenital CMV will have no signs or symptoms at all (known as “asymptomatic”) and will not develop any problems as they grow older.  Others may have no obvious signs at birth, but around 15% may go on to develop hearing loss over time.

Some children will be born with obvious symptoms of congenital CMV (“symptomatic”) and around half of these children will have one or more long-term impairments.  These may include hearing loss, cerebral palsy, seizures, ADHD, autism, developmental differences and learning delays, feeding issues or visual or sensory impairment.

Overall, around one in every four children born with the virus will have long-term problems such as hearing loss or developmental disabilities due to the infection.

Making the diagnosis after birth – what doctors will look for

If there is a possibility the CMV virus has been passed on, for example, mum has been diagnosed with a CMV infection in pregnancy, or a baby has failed the new-born hearing screening test, an early diagnosis is essential so that treatment can be considered.   These tests need to be done before the baby is 3 weeks old, to be sure if CMV was caught before or after birth.  If anti-viral treatment is needed, this should be started before the baby is four weeks old.  This may help to stop hearing loss from getting worse.

If there are signs of CMV infection, your baby’s doctor will test to confirm a diagnosis of congenital CMV (i.e. your baby caught it whilst in the womb).  However, some signs are not unique to congenital CMV and some babies will not show all these signs.

Some babies will have very obvious signs of CMV infection. These can include:

  • Lots of very small (1-2mm) red or purple spots (called petechiae)
  • Larger (2-8mm) red or purple dome shaped spots (called blueberry muffin rash)
  • Low birth weight, indicating poor growth during pregnancy
  • A head significantly smaller than other babies (microcephaly)
  • Enlarged liver and spleen (hepatosplenomegaly)
  • Yellow skin (jaundice).

Babies who fail their newborn hearing test should also be tested for CMV infection.

A saliva, urine or blood test can confirm whether the CMV virus is present. A positive test on a saliva sample will normally be confirmed with a urine test, to be sure of a positive result.   The sample must be taken within the first three weeks of your baby’s life to be sure that it is a congenital CMV infection, i.e. your baby caught it whilst in the womb. Otherwise they may have caught it during or after the birth, which won’t cause any long-term problems for full-term babies. Another reason for confirming the diagnosis within the first three weeks after birth is that treatment needs to begin within four weeks of life.

Further tests once congenital CMV is confirmed

Doctors may carry out further tests to see how your baby has been affected by the infection and whether they should be considered for treatment:

Blood count, platelet count & liver function tests

Congenital CMV can cause a reduction in the number of red and white blood cells and inflammation of the liver (hepatitis).

Brain scan

Congenital CMV can cause some distinctive changes to the brain which may affect your child as they develop. A brain scan can help doctors to diagnose congenital CMV infection and also consider whether treatment with anti-viral medication is appropriate. In some cases, it can help doctors to identify children who may be most at risk of developmental or hearing problems in the future. The doctor will decide on the most appropriate kind of scan (ultrasound, or MRI, or in some cases both) and discuss the results.

Hearing test

Hearing loss is one of the most common symptoms of congenital CMV. This test will be more detailed than the hearing screen carried out on all babies at birth and carried out by audiologist.

Eye test

This is to check for any inflammation or scarring on the retina (the light sensitive layer of tissue in the back of the eye). Some children may also have visual impairment caused by a brain problem rather than an eye problem.

Your baby should be referred to a paediatric infectious diseases consultant if congenital CMV is suspected.

Later Diagnosis

If your child tests positive for the CMV virus when they are more than three weeks old, it can be helpful to test the sample of blood that is collected from all babies in the UK when they are a few days old. This sample is called a Newborn Blood Spot (formerly the  Dried Blood Spot or Guthrie test). A positive result will confirm that the infection was caught before birth (a congenital infection).  However, this test is not perfect, in that it does not pick up all cases of CMV infection (it picks up 80-90%).  Therefore, a negative result cannot fully rule out congenital infection.