When you’re pregnant, you likely have concerns about the health of your unborn baby (fetus). One of those concerns may be infections that your baby can develop while in the womb. These are called congenital infections.

Cytomegalovirus (CMV) is a very common virus, and most babies who contract it have mild symptoms or no symptoms at all.

However, if you contract CMV very early in pregnancy and it’s passed to the fetus, that baby may experience more serious symptoms after birth, including hearing loss.

Here’s what you need to know if your baby has tested positive for congenital CMV.

If your baby is CMV-positive at birth, it means that they contracted CMV. It also means that you have CMV, and the virus crossed the placenta at some point during your pregnancy.

If you have CMV and you’re pregnant, there’s a 35 percent chance that you’ll pass it to the fetus.

CMV can cross the placenta at any point during pregnancy, but the earlier a fetus is exposed to a new CMV, the worse their symptoms will likely be.

A doctor may decide to test your baby for CMV if your baby has symptoms. It’s important to test babies who have signs or symptoms of CMV because early treatment for CMV may reduce some of the potential long-term effects of CMV infection in a baby — especially developmental delays and hearing loss.

Many babies with CMV will have no signs or symptoms. However, according to the Centers for Disease Control and Prevention (CDC), some babies born with CMV may have signs including:

Some babies born with CMV may have long-term health problems, such as:

Because CMV is common and doesn’t always cause symptoms, doctors don’t always test for it during pregnancy or after birth. During pregnancy, blood tests will be used to test for the presence of CMV.

Doctors may diagnose CMV in fetuses during pregnancy or after the baby is born. For this reason, attending regular prenatal appointment visits is very important. At these visits, a doctor may perform an ultrasound examination to check for atypical fetal development that CMV may cause.

Examples of ultrasound findings in a baby with CMV include:

If a doctor is able to perform serial ultrasounds and MRIs during a pregnancy, there’s a 95 percent likelihood that they’ll be able to identify atypical fetal brain development that may be consistent with CMV exposure.

An amniocentesis, or test of amniotic fluid, is used to detect CMV in unborn babies.

After a baby is born, doctors can diagnose CMV by collecting some form of bodily fluids. The fluid sample can be:

  • urine (preferred testing method)
  • blood
  • saliva

A healthcare professional must collect this sample within 2 to 3 weeks after a baby is born to most accurately diagnose the baby with congenital CMV rather than a CMV infection from after birth.

Questions for your doctor or healthcare professional

If you’re expecting or planning to be, here are some questions you can ask your doctor about CMV:

  • Should I have CMV testing?
  • How can I minimize my risk of getting CMV?
  • If my baby does have CMV, what are my next steps?
  • What should I be prepared for after delivery if my baby is CMV-positive?

The treatments for CMV in babies usually depend on whether the baby is symptomatic. If a baby is showing signs of CMV at birth, such as hearing loss, a doctor may prescribe antiviral medications.

An example of treatment is the medication valganciclovir. In symptomatic babies, this medication may improve a baby’s hearing development.

Antivirals for CMV may have serious side effects in babies, such as:

  • anemia
  • low platelet counts
  • low white blood cell counts

This is why doctors don’t prescribe them to all babies who are CMV-positive.

Since most people have no symptoms of CMV infection during pregnancy, testing is not routinely done during pregnancy. However, some researchers are investigating the use of antiviral medications like ganciclovir and valganciclovir to treat known CMV infections during pregnancy with the hopes of improving outcomes for exposed unborn babies.

The chief risk factor for CMV is having contact with children under 3 years old during pregnancy. Young children are the group most likely to carry CMV.

To reduce the risk of CMV transmission, parents and caregivers should avoid contact with the bodily fluids of young children, such as urine, saliva, and blood. This is especially true in the first trimester of pregnancy or up to 14 weeks.

Anyone who’s been around young children understands that avoiding contact with bodily fluids can be difficult. But some of the key preventive steps include:

  • not kissing young children on the lips
  • not sharing food or utensils with a child
  • washing your hands after each diaper change

The risks for CMV infections are greatest when the virus affects the baby in their embryonic period (first trimester). However, you’re less likely to pass CMV on to your baby at this time.

The outlook for babies born with CMV can vary because the virus affects babies in very different ways.

An estimated 90 percent of babies born with CMV have no symptoms at birth. While they may be born with the virus, they don’t have significant healthcare concerns because of their CMV. But they may have health concerns that appear later in life.

The effects that range from moderate to severe for babies born with CMV include:

In rare but severe, cases, CMV can result in miscarriage, stillbirth, or infant loss.

Although CMV is a common viral infection, it can cause serious side effects in babies. Taking steps to minimize CMV infection risks when pregnant may help you prevent CMV transmission, especially if you have young children and are at higher risk.

Regular obstetrician visits can help a doctor track the baby’s development and identify potential effects of prenatal CMV.