Cytomegalovirus (CMV) is a common illness that's usually not cause for concern. But getting it for the first time while pregnant can lead to complications like hearing loss, vision loss, and developmental delays in your baby. We spoke with experts to learn more.

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The majority of American adults will contract cytomegalovirus (CMV) before age 40. The virus is usually nothing more than a minor inconvenience. But if you catch CMV for the first time while pregnant, there's a greater risk that your baby will suffer complications such as deafness, blindness, and developmental delays

"We consider it a high-risk situation for the fetus if Mom gets infected for the first time during pregnancy. The reason is that the virus can cross the placenta and cause an infection in the fetus," explains Sallie Permar, M.D., Ph.D, chair of Pediatrics at Weill Cornell Medicine and NewYork-Presbyterian Komansky Children's Hospital, who is also on the board of directors at the National CMV Foundation.

CMV is actually the most common viral infection of the fetus during pregnancy. It affects between 0.2 and 2.2 percent of all babies born in the U.S., notes Santosh Pandipati, M.D., maternal-fetal medicine specialist at Obstetrix Medical Group of San Jose in California. He adds that CMV is the leading non-genetic cause of congenital deafness in the country. 

Keep reading to learn more about CMV infections while pregnant, including symptoms, complications, diagnosis, and more.

How Do You Get CMV During Pregnancy?

CMV is a herpes virus that spreads through close contact with bodily fluids like saliva, mucus, blood, urine, and semen, says Amy Banulis, M.D., an OB-GYN for Kaiser Permanente in Falls Church, Virginia. It's usually transmitted through activities like kissing or sharing utensils. 

As with all herpes viruses, once you're infected with CMV, it remains in your system forever. "It causes a latent infection that can reactivate later in life," says Dr. Banulis.

Most people get CMV during childhood, since it's easily spread among young kids. According to the Centers for Disease Control and Prevention (CDC), about one in three children under 5 have already contracted CMV, and more than half of American adults get infected before age 40. 

The chances of acquiring CMV while pregnant are slim, since most expectant parents have already had it. "It's estimated that 30-50 percent of pregnant women are susceptible to primary CMV infection in the U.S.," says Dr. Pandipati. "Of these women, 1-4 percent will experience a primary infection during pregnancy."

CMV Symptoms During Pregnancy

In healthy individuals, the majority of CMV infections are silent, but about 10 percent of people have symptoms, says Gail Demmler Harrison, M.D., a professor at Baylor College of Medicine and attending physician at Texas Children's Hospital, who has done research on CMV.

These symptoms present similarly to influenza or mononucleosis, and they include fever, swollen glands, sore throat, and fatigue. Immunocompromised individuals have a higher chance of CMV symptoms, adds Dr. Demmler Harrison.

Remember that most people acquire CMV before pregnancy, and inactive infections don't pose much risk to the fetus. But complications can occur when women get CMV for the first time while expecting, or if they have a reactivation.

Can CMV Infect Your Unborn Baby? 

In some cases, CMV can spread via the bloodstream and infect fetuses through the placenta (vertical transmission), says Dr. Pandipati. He adds that risk of vertical transmission depends on the trimester of maternal primary infection. Essentially, a mom infected with CMV during the first trimester transmits the virus to her baby less than 30 percent of the time. The risk of transmission is about 34-38 percent in the second trimester and 40-72 percent in the third trimester. 

CMV transmission to an unborn baby can sometimes cause complications. "Of those infected fetuses, 10-18 percent will be symptomatic at birth," says Dr. Pandipati. About 25 percent of these fetuses will develop complications of CMV by age 2, though consequences have been reported up to age 6.

It's important to note, however, that although transmission rate increases with each advancing trimester, the severity of complications tends to decrease. "The risk of transmission is highest in the third trimester, but it's less likely to cause consequences," explains Dr. Banulis. On the other hand, women infected in the first trimester have lower risk of transmitting CMV to their baby, but infection is more likely to cause complications. 

What happens if a woman already contracted CMV before her pregnancy? Usually it's not a problem at all. That said, if Mom experiences a CMV reactivation or reinfection while expecting, she can potentially transmit it to her baby, but the risk is lower than with a first-time infection. "It's usually estimated to be less than 1 percent," says Dr. Demmler Harrison. 

CMV Complications for Babies

If a baby is infected with CMV in utero, most cases are silent or asymptomatic. But about 10 to 18 percent of babies born with congenital CMV will have symptoms at birth—"and these babies have a much higher chance of having problems with their liver, blood counts, hearing, vision, and brain development," says Dr. Demmler Harrison.

Complications from congenital CMV can also show up down the road. For example, people infected in utero might suffer from progressive hearing loss late in life. 

CMV complications in babies include: 

  • Hearing loss ("CMV is the leading non-genetic cause of congenital deafness, affecting nearly 40,000 infants annually in the U.S.," says Dr. Pandipati.)
  • Vision problems 
  • Jaundice
  • Rash
  • Microcephaly (small head)
  • Low birth weight
  • Developmental delays
  • Enlarged liver and spleen
  • Seizures

"Among severely infected newborns, about 30 percent die, and 65-80 percent of survivors have severe neurologic disability," says Dr. Pandipati. 

Diagnosing CMV During Pregnancy

Certain tests look for CMV antibodies in a pregnant person's blood, says Dr. Permar. A IgG antibody test will indicate if an individual had CMV at some point in their life, while an IgM antibody test shows recent CMV infection. "Mom might have CMV antibodies from a past infection, so in order to see whether it's a new infection, the test has to be repeated to look at antibody levels to see if they're changing over time," explains Dr. Banulis

You can also test for CMV during pregnancy with amniocentesis—a procedure that involves removing amniotic fluid from the uterus and analyzing it. "Amniotic fluid is sent for PCR analysis to detect presence of CMV. Testing is most useful at 21 weeks or later, and ideally more than six or seven weeks from primary maternal infection," explains Dr. Pandipati. Also, in rare cases, the fetus can have blood tests done by a maternal fetal medicine specialist, explains Dr. Demmler Harrison.

CMV testing during pregnancy isn't universal, and it "generally occurs after suspicious findings are seen on routine prenatal ultrasound performed around 18-22 weeks gestational age," says Dr. Pandipati. Suspicious findings might include fetal growth restriction, small head size, brain cysts, enlarged liver, fluid around the abdomen or heart, bright appearance to the intestines, and more. 

Doctors can also test babies for CMV after birth. It's a fairly straightforward process that determines if the virus is being shed through urine, saliva, or blood. Dr. Permar explains that congenital CMV testing should only be completed in the first two or three weeks of life, because after that, it's hard to determine when your baby got infected (for example, did they get CMV in utero or from a sibling?)

Treatment for CMV During Pregnancy

When it comes to congenital CMV, there's nothing that will reduce the transmission risk to the baby. And there's no treatment for an infected baby in utero, says Dr. Banulis. It's more of a "watch and wait" situation that entails handling complications after birth. 

That said, there are some experimental treatment options that might reduce the risk of transmission to the fetus; these include CMV hyperimmune globulin and an antiviral called valacyclovir. These aren't standard approved treatments, so make sure to discuss them with your OB or maternal-fetal medicine specialist

It's important to keep in mind that most CMV infections don't cause symptoms in the mother, and most don't transmit to the fetus.

Treatment for CMV in Babies After Birth

If your baby is born with CMV, they might be treated with antiviral medications like intravenous ganciclovir or oral valganciclovir. "These antiviral medications may improve CMV symptoms immediately, and also reduce the risk of later problems, such as hearing loss and developmental problems—at least in the first few years of life," says Dr. Demmler Harrison. 

That said, according to the CDC, "Valganciclovir can have serious side effects and has only been studied in babies with signs of congenital CMV infection. There is limited information on the effectiveness of valganciclovir to treat infants with hearing loss alone." Your doctor can help you determine whether these treatments are recommended in your case.

If your baby has long-term effects of CMV, such as hearing and vision loss, therapies might be recommended. "Hearing loss can also be helped with hearing aids and cochlear implants," adds Dr. Demmler Harrison.

Preventing CMV Infection While Pregnant

While you can't eliminate all risks of getting infected with CMV while pregnant (vaccines are still being developed), the best way to protect unborn babies is practicing good hygiene, such as washing hands often with soap and water. Dr. Banulis recommends extra precautions for pregnant women who are often around children, like in a daycare setting. They should consider wearing gloves when changing diapers and avoid contact with urine or saliva. If you're worried about CMV infection, see your doctor for a blood test.