Originally published 19 October 2020. Revised October 2026.

Update note: This post has been reorganised and checked against current sources. The main changes: several figures in the original were wrong or muddled and have been corrected (in particular the transmission rate after primary infection and the proportion of infants affected), non-primary infection is now covered, and there is new material on screening, hygiene advice, treatment and vaccine status.

Cytomegalovirus (CMV) is the most common congenital infection (TORCH) and a leading non-genetic cause of sensorineural deafness in children. There is no vaccine. A phase 3 trial of an mRNA vaccine failed to meet its primary efficacy endpoint in October 2025, and the developer discontinued its congenital CMV program.

How it spreads and what it does to the mother

• CMV is excreted in saliva and urine, and in other body fluids. Shedding can continue for months to years, and it is most frequent in children under two, particularly those in day care.
• Most women with acute (primary) infection have no symptoms. When there are symptoms, they are usually a flu-like or mononucleosis-like illness, with fever and lymphadenopathy.
• The virus then becomes latent for life. It can reactivate, and a person can also be re-infected with a different strain. This is usually silent, except in the severely immunocompromised.

Who is at risk in pregnancy

• About 40% of Australian women of childbearing age are seronegative, so they can acquire a primary infection during pregnancy.
• Mothers of young children and women working in childcare are at higher risk, because they have the most contact with infected saliva and urine.

Risk to the baby

• Primary maternal infection carries the highest risk. The risk of transmission to the fetus is roughly 30% to 40%, and the risk of severe fetal or newborn complications is greatest with first-trimester infection.
• Non-primary infection (reactivation or re-infection in a woman who was already immune) carries a lower risk of fetal infection, about 1% to 3%. But the consequences can be as severe as after a primary infection. This is why immunity before pregnancy does not make the baby completely safe.
• Most infected babies look well. About 90% are healthy at birth with normal development, and around 10% overall have some disease at birth.
• Late problems: 10% to 15% of infected infants who are well at birth go on to have problems in later childhood. Hearing loss is the commonest, and overall about one in ten infected infants has a significant long-term impact (including hearing loss, developmental delay, epilepsy and cerebral palsy).
• In symptomatic cases, multisystem disease can include hearing loss and microcephaly, among other neurological problems.

Testing

• Universal serological screening in pregnancy is not recommended. The Australian Pregnancy Care Guidelines suggest a CMV IgG at the first antenatal visit for women at higher risk (for example, mothers of young children or those working in childcare).
• A woman with a compatible illness should have IgG and IgM, with IgG avidity added if both are positive. Primary and non-primary infection cannot be separated on serology alone.
• Amniocentesis is used to confirm fetal infection.
• Universal newborn screening is not done in Australia. Babies who fail the newborn hearing screen should be tested for CMV.

Prevention: hygiene advice for all pregnant women

Simple hygiene measures have been shown to reduce the risk of maternal infection. Offer this advice to every pregnant woman, whatever her serostatus, and ideally before conception.

• Do not share food, drinks or utensils used by young children.
• Do not put a child’s dummy in your mouth, and avoid saliva when kissing a child.
• Wash your hands thoroughly with soap and water for 15 to 20 seconds, especially after changing nappies, feeding a young child or wiping a child’s nose or saliva.
• Clean toys, benchtops and surfaces that touch a child’s urine or saliva, and do not share a toothbrush with a young child.

Treatment

• In pregnancy: there is no established or recommended treatment to prevent fetal infection after maternal primary infection, and options are evolving. High-dose valaciclovir given after first-trimester primary infection reduced fetal infection by about 70% in one trial, with adverse events in 3% of treated women (including 2% with acute renal failure that resolved on stopping). It is not standard in Australia, so involve maternal-fetal medicine and infectious diseases early.
• In the infant: valganciclovir for six months is recommended for infants with moderate to severe symptoms. Antivirals started in the first weeks of life modestly improve neurodevelopmental outcomes for the severely affected.

References

1. Overview of TORCH infections. UpToDate. https://www.uptodate.com/contents/overview-of-torch-infections
2. Birth prevalence, clinical sequelae and management of congenital cytomegalovirus. Med J Aust. 2025;223(11). https://www.mja.com.au/journal/2025/223/11/birth-prevalence-clinical-sequelae-and-management-congenital-cytomegalovirus
3. Cytomegalovirus in Pregnancy: Why It Matters. O&G Magazine. https://www.ogmagazine.org.au/?p=32307
4. Prevention of congenital cytomegalovirus infection (March 2019). Women’s Health, Counties Manukau. https://www.chl.co.nz/wp-content/uploads/2021/11/Prevention_of_congenital_cytomeglovirus_infection_March_2019.pdf
5. Moderna. Phase 3 CMV vaccine readout reflections (22 October 2025). https://www.modernatx.com/media-center/all-media/blogs/phase-3-cmv-vaccine-readout-reflections