Virus that can damage hearing in newborns detetectable via NIPT

Cytomegalovirus (CMV), a virus that can cause hearing loss and other neurodevelopmental delays in infants, can now be detected during prenatal screening.

Scientists in Belgium were able to detect CMV using data collected from non-invasive prenatal testing (NIPT). Previously, widespread prenatal screening for CMV was not considered useful because the infection could not be safely prevented. However, the drug valacyclovir has now been found to be safe and effective during pregnancy to prevent transfer of CMV to the fetus.

'Our study is the first to directly link [NIPT]-derived CMV read counts to both maternal serostatus and confirmed CMV outcomes from a systematic newborn screening program,' the authors wrote in their article published in Clinical Chemistry. 'Higher read counts are predictive of both primary maternal infection and congenital transmission, enabling the definition of clinically valid thresholds to identify pregnancies eligible for valacyclovir therapy.'

The study used retrospective NIPT data that were collected at 12 weeks gestation. NIPT looks at fragments of cell-free DNA present in the mother's blood – these include her DNA and the fetus's, and is used to detect chromosomal abnormalities in the developing fetus. This blood can also contain viral DNA if the mother has an infection. The CMV screening was developed to identify and quantify these fragments to estimate the mother's viral load.

The study detected CMV in about two percent of the pregnancies tested, and the authors found that a higher viral load was associated with a greater chance of infection in the fetus. Up to 20 percent of infants who had a CMV infection in utero went on to develop permanent hearing loss or other effects from the infection.

CMV is a common virus that seldom causes symptoms in adults, but can cause children to be born deaf or lose their hearing in early childhood. Globally, CMV is found in around one in every 150 pregnancies, making it one of the most common infections in pregnancy. It is also the second most common cause of childhood hearing loss after genetic forms of deafness, and around 20 percent of affected infants also present with neurodevelopmental delays.

The largest risk of CMV causing hearing loss occurs when the virus is passed to the fetus during the first trimester of pregnancy. NIPT is typically offered around the end of the first trimester but as CMV infection can happen at any stage, the authors suggest routine viral checks for the duration of the pregnancy.