About 50% to 85% of adults in the United States will become infected with CMV by the time they turn 40. About half of expectant mothers have never been infected with CMV. About 1% to 4% of uninfected mothers have primary CMV infection during their pregnancy.
If a pregnant person has never been exposed to CMV and has their first infection during pregnancy, there is a chance that the fetus could become infected before the body can eliminate the virus. About one third of those who become infected with CMV for the first time during pregnancy pass the virus to their unborn babies. Thus, CMV is the most common cause of congenital viral infection in the United States.