CMV (Cytomegalovirus) and pregnancy
By Dr Guy SKinner
CMV is the most common damaging infection in pregnancy. Many people are fearful of the risk of Listeria from contaminated food during their pregnancy, but this is actually a rare problem in pregnancy. CMV however, is often the hidden cause of significant morbidity in new-borns and is the most common, non-genetic, cause of deafness in Australia.
What is CMV?
CMV is a common virus spread easily via body fluids affecting many humans in the early toddler years. Child care centres are a particularly high place of carriage of the virus. More than fifty percent have been infected by the end of schooling and 85% by 40 years of age. Most infections are asymptomatic so screening high risk groups is the only way of possible detection. The first (primary) infection has the greatest risk of fetal infection, whilst reactivation of previous infection has a low-risk of transmission to the baby. Symptons such as fever or swollen glands are rare in primary infection for adults. Even toddlers may have mild fevers or tiredness and this is generally indistinguishable from other general viral infections.
Who is at risk?
The highest prevalence of active CMV infection is amongst toddlers. Therefore pregnant women who are infrequently around toddlers have a very remote risk of CMV. Second or subsequent pregnancies for women have a much higher risk of primary infection for the unborn child. These are the women I screen to determine if they have been exposed previously and subsequently have a relative immunity. Approximately 20% of these second time mothers have no immunity and are most at risk, and currently 10% of these women get a primary infection during their pregnancy. When a primary infection occurs in pregnancy significantly alters the risk of transmission to the baby and the type of complications the baby may get. The timing when the mother gets CMV in the first trimester, the potential consequences of deafness, blindness, intellectual disability and small brain are highest. If the maternal infection is in the second or third trimester, the risk of infection to the baby may be between 50%-70%, but the risk of serious long-term problems is lower than during the first trimester. In the late third trimesters, fetal infection can affect the baby’s liver, spleen, lungs or even blood production. Of the infected babies, 10% have clear complications at birth. Of the 90% who don’t have sign of infection, 20% will still develop long term deafness during childhood.
What can be done to prevent CMV?
Finding which pregnant women with exposure to toddlers who have never had the CMV virus previously will identify who is most at risk. As the virus is spread by body fluids (all fluids), avoidance of these fluids is the most effective method to prevent primary infection. There is currently no vaccine, and no effective anti-viral treatment for mothers. Avoiding contact with saliva, mucous, urine or other body fluids with the toddler is the best protection. Not sharing food, drink bottles and thorough hand washing with soap after nappy changes is also an effective prevention strategy. Avoid contact with saliva when kissing children, and utilise cleaning agents on toys and bench tops if contaminated with body fluids. Child care workers are particularly at risk, however, most have been exposed very early on in their careers.
How is CMV diagnosed?
Maternal blood tests can determine if current or previous exposure has occurred. If maternal infection has occurred in the first trimester, then reliable detection of the fetus being infected cannot be made until as late as 20 weeks gestation when an amniocentesis (needle extractions of amniotic fluid) is performed to find if CMV is found as the pure virus from the baby’s urine production. This is obviously very late in the pregnancy and causes considerable stress for the parent. Many of the complications of CMV cannot be detected during the pregnancy, and prognosis cannot be accurately determined.
Currently, treatment for the baby post birth is mainly supportive and doesn’t appear to alter long-term outcomes. Some antiviral treatment maybe tried but this doesn’t always alter the prognosis.
What is the recommended policy of CMV prevention?
Currently the State and Federal health authorities do not have a formal plan to reduce CMV effect on unborn babies. I believe identifying women most at risk of developing CMV during primary infection in their pregnancy, and introducing strategies to reduce their exposure is current best practice.
