Chances of fetal infection and harm
The chance of fetal CMV virus infection depend on the week of maternal infection. If the mother was infected in the first trimester of the pregnancy, the chances of fetal infection reach approximately 35%.
It is important to stress the fetal CMV infection does not necessarily indicate fetal illness and in fact, about 85% of infected fetuses will be carriers of the virus without symptoms (asymptomatic). (2)
If infection occurs around the time of conception, the fetal chances of infection go down dramatically, and they grow smaller the more distant the time of the infection is from the time of conception (i.e. prior to conception).
The more advanced gestational stage when the mother is infected, the greater the risk for fetal infection with the CMV virus, but the risk for serious fetal injury goes down. The fetus body systems are more developed and therefore less exposed to the virus’ adverse effects, so infection in the third trimester will be inconsequential in most cases.
If there is injury due to fetal infection with CMV, it can manifest in a wide range of symptoms.
However, in the first trimester, out of the 15% of the fetuses affected by the infection, only half the fetuses will develop serious injuries, while the other half will suffer from minor injuries that can be treated, and some are reversible.
Therefore, a simple statistical calculation will show that out of all women infected with the CMV virus for the first time in the first trimester, only about 3% of the fetuses will develop serious injuries, such that according to recent studies, can usually be identified in virus targeted ultrasound scans.
The use of the term serious injuries relates mainly to findings in the ultrasound scans that suggest a serious disease that can cause intellectual disability, significant developmental delay, blindness and various neurological problems.
In serious cases of infection during early pregnancy, there is also risk of intrauterine fetal demise as a result of the virus’ effect.
The use of the term mild injuries relates mainly to hearing injuries, which cannot be identified in scans.
About 10% of the infants who are infected with the CMV virus during pregnancy will develop hearing injuries. The injuries mat range between total deafness, which is very rare, and mild injuries to one or both ears.
In Israel, a baby born with a profound hearing impairment can have a cochlear implant surgery at the age of one year, which will enable him to hear, and babies with a different hearing range injury may benefit from hearing aids. A baby born with a hearing impairment can receive drug treatment that may stop hearing deterioration and in some cases even improve the hearing that was impaired due to the virus. You can read about the drug treatment under the tab Birth and time in the neonatal Department.