Cytomegalovirus (CMV)

This page shares information from what we've learned along our journey and from medical professionals and experts in the field. This is our family’s experience in Aotearoa New Zealand. We ourselves are not medical professionals, and this is not medical advice.

Understanding CMV

CMV (cytomegalovirus) is a very common virus. Most people will be infected at some point in their lives — often with mild symptoms or none at all. For most people, CMV is harmless. But CMV it can be more serious during pregnancy.

However, CMV can be more serious if a person is infected for the first time during pregnancy.

When a baby is infected during pregnancy, this is called congenital CMV (cCMV).

How common is congenital CMV?

Congenital CMV is recognised worldwide as the most common congenital infection.

Large international reviews estimate that cCMV affects approximately:

0.5%–0.7% of live births
Roughly 1 in every 200 babies

An important and often misunderstood point:

The number of babies officially diagnosed with cCMV is likely much lower than the true number of babies actually born with it.

Why?

Many babies with cCMV look completely well at birth
CMV is not routinely tested for in most newborn screening programs (including in New Zealand)
Some effects - especially hearing loss - can appear months or even years later

In some countries, only a small number of cases are formally reported each year through clinician notification systems — far fewer than expected based on population estimates.

This suggests that cCMV is frequently under-identified and under-recorded.

Many babies with congenital CMV:

Have no obvious symptoms at birth
Pass their newborn hearing screen
Appear completely healthy

However:

Hearing loss can develop later (late-onset)
Hearing loss can worsen over time (progressive)

This delayed impact is one reason CMV can feel so shocking for families. You may do “everything right,” pass early checks, and only discover CMV after a hearing loss diagnosis.

CMV during pregnancy

The timing of infection during pregnancy can influence outcomes.

Infection in the first trimester is more strongly associated with higher risk of long-term complications
Infection later in pregnancy can still result in congenital CMV, but severe outcomes may be less common
Both primary (first-time) infections and reactivation/reinfection can lead to transmission to the baby

Not every baby exposed during pregnancy will be affected. And not every affected baby will have severe outcomes. The range is wide, from no symptoms at all to significant medical needs.

Prevention

CMV spreads in the same way many common viruses and bugs do - through close contact with bodily fluids such as saliva, urine, tears, and mucus. This is why it is especially common around young children, who often carry CMV without any symptoms.

CMV is still relatively unknown to many people, and its potential impact during pregnancy is often not widely discussed. At the same time, pregnancy already comes with a long list of “do’s and don’ts,” and adding another virus to worry about can feel overwhelming.

This is not about creating fear or blame. Most people who have CMV during pregnancy had no major symptoms and no idea they were infected, or just passed it off as a cold or flu.

But awareness matters and simple hygiene habits, especially when around toddlers, may help reduce risk, including:

Careful handwashing (particularly after nappy changes or wiping noses)
Avoiding sharing food, drinks, or utensils with young children
Avoiding contact with saliva where possible

There is currently no licensed CMV vaccine.

CMV and hearing loss

Congenital CMV is widely described as the leading non-genetic cause of childhood sensorineural hearing loss.

Key things families are often not told early enough:

Hearing loss can affect one ear (unilateral) or both ears (bilateral)
It can be present at birth or appear later
It can be progressive, changing over time

Research and clinical guidance commonly estimate that around 10–15% of babies with congenital CMV develop hearing loss - including some who seemed completely well at birth.

Possible impacts of congenital CMV

Most babies with cCMV will not experience severe complications.

However, for some babies, congenital CMV can be associated with:

Miscarriage or stillbirth
Premature birth
Low birth weight
Brain development differences
Microcephaly (small head size)
Brain injury or brain damage
Seizures or epilepsy
Developmental delay
Cerebral palsy
Vision problems
Feeding difficulties
Hearing loss (unilateral, bilateral, late-onset, or progressive)

Estimates from public health agencies suggest that approximately 1 in 5 babies born with congenital CMV may experience birth defects or longer-term health challenges.

The spectrum is broad, some children are profoundly affected, while others may only experience hearing differences.

Testing and diagnosis

For congenital CMV, early testing is important.

Diagnosis typically relies on confirming infection within the first few weeks of life. After that window, diagnosis becomes more complex and may require retrospective testing (for example, using stored newborn screening samples in some countries, including New Zealand).

Importantly: CMV is not routinely included in standard newborn screening programs in many countries, including New Zealand.

This is one reason families often only learn about CMV after a child develops hearing loss or other symptoms.

Treatment in newborns

If congenital CMV is diagnosed very early in a baby’s life, there is an antiviral medication that may be offered in some situations.

The medicine (most commonly valganciclovir) works by slowing down the virus in the body. When started early, it may help reduce the risk of hearing loss getting worse and may support developmental outcomes in some babies.

However:

It does not cure CMV
It does not guarantee that hearing loss or other effects won’t happen
It is usually only offered to babies who show symptoms
It can have side effects and requires careful monitoring by doctors

Treatment decisions are made by specialist teams who carefully weigh the possible benefits and risks for each baby.

Because this medication is only considered in the early weeks of life, early diagnosis can make a difference.

Follow-up and monitoring

Because CMV-related hearing loss can; appear later, change over time and affect one or both ears, clinical guidance commonly recommends ongoing audiology monitoring for children diagnosed with cCMV.

If hearing loss does present itself it is better to learn this early and look at what options there are to help.

Resources