There are many frustrations in the management of CMV infection in pregnancy. Unlike many other infectious diseases—such as rubella (German Measles), toxoplasmosis and chickenpox—there are few prevention and treatment options for CMV.
CMV is the largest of the Herpes virus family. Like all Herpes viruses, a first or ‘primary’ infection can occur at any time, but it may also remain ‘latent’ to be re-activated later in life. This can happen for example in someone whose immune system is suppressed, or if they have experienced a stressful stimulus, in which case it is known as a ‘secondary’ infection.
Estimates vary by ethnic group, but overall around three out of every five people13 in the UK have been infected with CMV at some point in their life, usually early on.
This leaves around two in every five pregnant women susceptible to a primary infection, and between one and four out of every hundred pregnancies will see a mother infected by CMV for the first time.29 Of those who become infected when pregnant, almost a third (32 per cent)30 will transmit the infection to their unborn baby. Once infected, up to 15 per cent2 of unborn babies will show signs of disease, and a similar proportion of babies who have no symptoms at all will go on
to develop permanent problems,2 of which the most common is hearing loss.
32% will transmit the infection to their unborn baby.
CMV infection during pregnancy is most often suspected and diagnosed when an ultrasound scan shows suspicious features. These include the baby being small, with low amniotic fluid (oligohydramnios), echogenic (bright) kidneys and in some cases brain abnormality (usually water on the brain or hydrocephalus). Such cases are usually referred to a specialist fetal medicine centre where a detailed scan can be performed by an expert. Since testing the mother’s blood can produce inconclusive results, the majority of experts will want to perform an amniocentesis test to identify CMV DNA, and also look for other signs such as a low platelet count in the baby’s blood.
In such cases, treatment options are limited, and even when treatment is administered it may not prevent damage to the baby. The use of antiviral medicines such as ganciclovir (either by treating the mother or directly into the baby by in-utero transfusion) may reduce the amount of circulating virus, and improve platelet count and liver function tests in the baby. However once damage has occurred it is unlikely to be reversed. Currently there is little high quality or definitive evidence on the most effective ways to treat CMV infection in pregnancy. There have been no randomised controlled trials proving that antiviral treatment works and reduces handicap rates, and more research studies are urgently needed.
Public health measures are urgently needed to reduce the risks of infection
Routine screening for CMV during pregnancy is not performed in the UK. The National Screening Committee has recommended against CMV screening in the antenatal period, because there is uncertainty about the risk to the baby when maternal infection is diagnosed and because the effectiveness of treatment has not been confirmed. However, the consequences of this infection in pregnancy can be devastating. Public health measures are urgently needed to reduce the risks of infection in high risk individuals in particular (for example pregnant health care workers, teachers, and women with young children), and all pregnant women should be routinely counselled about the need for hygiene and avoidance of contact with small children’s saliva and urine during pregnancy.
In reality, however, it is hard to avoid every possible exposure, and there is certainly a need for more research into the development of vaccines which could be safe and effective in women of reproductive age. In the meantime, more understanding of the pathogenesis of susceptibility, infection and transmission to the unborn baby during pregnancy can only help in improving outcomes in this little-known but potentially devastating disease process.
Professor Mark Kilby
Clinical Scientist and Honorary Consultant in Fetal Medicine, Birmingham Women’s Foundation Trust