Congenital CMV infection: risks, prevention and testing

Cytomegalovirus belongs to the herpes virus family. The NHS describes it as common and usually harmless, and Tommy's notes that most people have been infected at some point and carry the virus for life. It spreads through close contact with body fluids such as saliva, urine, blood, breast milk and genital secretions.

Small children in nurseries and playgroups often shed the virus for months in saliva and urine without being ill, which is why parents, nursery staff and early-years workers are the groups most often exposed.

A baby can pick up the virus across the placenta if the mother has a first infection during pregnancy, or less often when a past infection reactivates or she catches a different strain. This is called congenital CMV. The NHS says the virus is particularly dangerous to a baby when the mother has not had the infection before.

Most mothers who are infected have no symptoms or a mild flu-like illness. Because infection often goes unnoticed, many cases are only recognised when a newborn is tested.

Most babies who are born with CMV remain well. The NHS lists the possible effects in affected babies as rash, jaundice, low birth weight, a small head, seizures, hearing loss, eye problems and enlargement of the liver or spleen. The NHS pregnancy infections page also mentions visual impairment or blindness, learning difficulties and epilepsy.

Tommy's says around 10% of infected babies show symptoms at birth, and roughly half of those have long-term problems, frequently hearing impairment. Some babies who look well at birth can develop hearing loss later, so hearing follow-up matters even when the newborn check is normal.

The advice is practical and based on avoiding contact with saliva and urine from young children. It matters most for women who already have toddlers or who work in childcare.

• Wash your hands with soap and warm water after changing nappies, wiping noses or handling toys.

• Do not share food, cutlery, drinks or a dummy with young children, and do not put a child's dummy in your mouth.

• Kiss and cuddle on the head rather than on the mouth or cheek.

• Clean toys and surfaces contaminated with saliva.

• If you work with young children, ask your employer or occupational health about additional measures.

Tommy's reports that the UK National Screening Committee does not recommend routine CMV screening in pregnancy or for newborns, although the position is being reviewed as evidence emerges. Testing is therefore usually offered when something prompts it, such as a flu-like illness, an ultrasound finding, or a newborn failing the hearing screen.

A blood test can show whether you have had the infection before. If recent infection is suspected, a fetal medicine specialist may discuss further tests and ultrasound. If a baby is suspected of having congenital CMV after birth, testing must be done within the first weeks of life to separate congenital from later infection.

The NHS says there is currently no treatment for CMV in pregnancy, and that most pregnancies proceed without complications. Tommy's adds that the antiviral valaciclovir may reduce the chance of transmission when a first infection happens in early pregnancy, which is a decision for a specialist and not something to start alone.

For babies with confirmed congenital CMV, paediatric specialists decide whether antiviral treatment is appropriate and arrange hearing, vision and developmental monitoring. Hearing aids, cochlear implants and early education support can change outcomes for children with lasting hearing loss.

Tell your midwife or GP if you develop a flu-like illness that does not fit another explanation, or if you are in regular contact with someone known to have CMV. Do not panic: a single exposure does not mean the baby is affected, and most infections do not cause harm. Your maternity team can decide whether testing is helpful and can refer you to fetal medicine if needed.