The risk of hearing loss due to congenital cytomegalovirus (CMV) infection is greater when the mother-to-be is infected with the virus in the first three months of pregnancy rather than later in the pregnancy, researchers have found.

More than half of the population is infected with CMV, a type of herpesvirus. The virus rarely causes symptoms in adults with healthy immune symptoms. However, CMV can cause problems when passed from a mother to a fetus during pregnancy.

Congenital CMV infection is the most common viral infection affecting the fetus, Dr Ina Foulon and colleagues from Universitair Ziekenhuis in Brussels, Belgium, note in their report. In a previous study, they found that children with congenital CMV had a risk of 22 per cent of developing sensorineural hearing loss, which is hearing loss due to nerve damage.

In their latest study, the researchers examined the association between CMV infection occurring at different times of pregnancy and sensorineural hearing loss in 34 children who were diagnosed with congenital CMV infection. Of these children, five were lost to follow-up and one died.

Of the 28 remaining children, sensorineural hearing loss occurred in four of the five children (80 per cent) born after maternal CMV infection occurring in the first trimester and one of the 12 children (eight per cent) born after maternal CMV infection in the second trimester.

Sensorineural hearing loss did not occur in any of the children born after maternal CMV infection occurring in the third trimester.

Progression of sensorineural hearing loss was observed in two children born after a maternal CMV infection of the first trimester.

The vulnerability of hearing to early CMV infection in the womb may be explained by the embryological development of the ear, the investigators explain, which largely occurs between the third and 10th week of gestation.

Reuters

Source: Pediatrics, December 2008.