CMV, or cytomegalovirus, is a common virus that most adults carry without knowing it. When a baby is born with the infection, passed from mother to child during pregnancy, it’s called congenital CMV. About 1 in 200 babies is born with it, making it one of the most common congenital infections. Most of these babies will be perfectly fine, but roughly 1 in 5 will develop birth defects or long-term health problems.
How a Baby Gets CMV Before Birth
CMV belongs to the herpesvirus family, which means once someone is infected, the virus stays in the body for life. It usually sits dormant in cells without causing any noticeable illness, but it can reactivate from time to time. A pregnant woman can pass CMV to her baby in three ways: through a first-time infection during pregnancy, through reinfection with a different strain of the virus, or through reactivation of a previous infection.
The risk to the baby depends heavily on which scenario applies. A first-time (primary) infection carries the highest transmission rate: 30 to 40% in the first and second trimesters, rising to 40 to 70% in the third trimester. Reactivation or reinfection is far less likely to reach the baby, with a transmission rate around 3%. The timing matters too. A primary infection in the first trimester poses the greatest risk of serious complications, because that’s when the baby’s brain, eyes, and organs are forming most rapidly.
Signs of CMV at Birth
Most babies born with congenital CMV show no obvious signs at all. They look healthy, pass their initial checkups, and go home without anyone suspecting an infection. This is one of the things that makes CMV tricky: the majority of cases are invisible at birth.
Babies who do show symptoms can have a range of problems, including:
- Jaundice: yellowing of the skin or the whites of the eyes
- Microcephaly: an unusually small head, which can signal problems with brain development
- Low birth weight
- Enlarged liver and spleen
- Rash
- Seizures
- Retinitis: damage to the retina in the eye
Babies with visible symptoms at birth are more likely to face long-term challenges, but even some babies who appear healthy initially can develop problems later.
Hearing Loss and Other Long-Term Effects
Hearing loss is the most well-known complication of congenital CMV, and it’s also the most common non-genetic cause of hearing loss in children. What makes it particularly difficult to catch is that it doesn’t always show up right away. A baby can pass their newborn hearing screen and still develop hearing loss months or years later. In one large study, about 6% of ears with normal hearing at birth went on to develop late-onset hearing loss, sometimes beyond four years of age.
This delayed onset means a single hearing test at birth isn’t enough. Children with confirmed congenital CMV typically need regular hearing evaluations well into early childhood to catch any changes as they emerge. Early detection matters because hearing loss during the first few years of life can significantly affect speech and language development.
Beyond hearing, congenital CMV can also cause vision problems, learning difficulties, and in more severe cases, developmental delays or intellectual disability. These outcomes are more common in babies who were symptomatic at birth, but they can occasionally appear in children who initially seemed unaffected.
How CMV Is Diagnosed in Newborns
Testing for congenital CMV is straightforward: a saliva or urine sample from the newborn is checked for the virus. The key detail is timing. The test needs to happen within the first few weeks of life. After that point, a positive result could reflect a CMV infection picked up after birth (from breast milk or close contact) rather than one acquired in the womb, and the distinction matters because congenital infection carries different risks.
Right now, most babies in the United States are not routinely tested for CMV at birth. Many states have adopted targeted screening, meaning babies who fail their newborn hearing test are then tested for CMV. Several major medical organizations, including the American Academy of Otolaryngology and the American Academy of Audiology, have recommended expanding to universal screening for all newborns, but this has not yet become standard practice everywhere. The gap means that many asymptomatic babies with congenital CMV are never identified.
Reducing the Risk During Pregnancy
There is no vaccine for CMV. Prevention during pregnancy centers on hygiene, particularly around young children, who are among the most common sources of the virus. Toddlers in daycare frequently carry CMV in their saliva and urine, often with no symptoms of their own.
Practical steps include washing your hands thoroughly after changing diapers or wiping a child’s nose, not sharing utensils or cups with young children, and avoiding kissing toddlers on the mouth where saliva contact is likely. These measures are logical and widely recommended, though it’s worth noting that they haven’t been definitively proven in clinical studies to reduce congenital CMV rates. They remain reasonable hygiene practices that lower exposure to CMV and many other infections during pregnancy.
Women who work in childcare settings or who have a toddler at home while pregnant face the highest exposure risk. CMV spreads through bodily fluids (saliva, urine, blood, breast milk), so any situation involving frequent contact with these fluids increases the chance of a first-time infection.
What Happens After a Diagnosis
When a baby is diagnosed with congenital CMV, the next steps depend on whether symptoms are present. Babies with signs of infection at birth are typically evaluated with brain imaging, eye exams, and hearing tests to understand the full scope of the infection’s effects. Antiviral treatment may be offered for symptomatic infants, with the goal of improving hearing and developmental outcomes.
For babies diagnosed with congenital CMV but no symptoms, the approach is usually monitoring rather than treatment. Regular hearing tests over the first several years of life are the cornerstone of follow-up, since late-onset hearing loss remains a real possibility. If hearing loss is detected early, interventions like hearing aids or cochlear implants can make a substantial difference in a child’s language development.
Many children with congenital CMV, even some who were symptomatic at birth, go on to develop normally. The range of outcomes is wide, which is why ongoing monitoring gives families the best chance of catching and addressing any problems as they arise.