Infection with cytomegalovirus (CMV) is mainly caused by close physical contact.
CMV is a common virus that is related to the viruses that cause chickenpox and glandular fever.
Congenital CMV is where a mother passes a CMV infection on to her unborn baby.
Some cases occur when a pregnant woman is infected by CMV for the first time during, or shortly before, pregnancy (a primary infection). In around 3 out of 10 cases, the baby will also be infected.
In some cases, a previously inactive CMV infection can recur during pregnancy. The mother could also be reinfected with another strain of the CMV virus, which can be passed to her unborn baby.
In the majority of cases, the virus doesn't harm the baby. However, in severe cases, it can interfere with the baby’s normal development, resulting in the associated disabilities and symptoms of congenital CMV.