Understanding CMV (Cytomegalovirus)

Shannon M. Clark, MD
May 6, 2022
Understanding CMV (Cytomegalovirus)

*Updated 10/2022

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But today, I want to share with you information about a virus that can affect pregnancy which many do not know about: Cytomegalovirus–also known as CMV.

What is CMV?

In this video, I share an overview of what CMV is and statistics about the virus. According to the CDC, “CMV, is a common virus that infects people of all ages. Over half of adults have been infected with CMV by age 40. Most people infected with CMV show no signs or symptoms. When a baby is born with cytomegalovirus (CMV) infection, it is called congenital CMV.”

CMV is the most common congenital infection, occurring in 0.5-1.3% of all births via vertical transmission from the infected pregnant person to the fetus through the placenta. That equates about one out of every 200 babies or 40K babies a year in the U.S. It is the leading cause of deafness due to non-genetic causes. However, routine screening during pregnancy is not recommended.

Fetal Infection

Why isn’t routine screening for this virus during pregnancy recommended?

According to the SMFM’s Choosing Wisely list, routine screening of CMV during pregnancy is not recommended due to poor predictive value of the available tests and potential for harm due to false positive results. Other reasons include:

  • Maternal antibody screening in pregnancy cannot differentiate primary from recurrent infection and the results are difficult to use in counseling patients about fetal risk.
  • Maternal immunity on blood testing does not eliminate the possibility of fetal infection with up to 75% of congenital CMV infections worldwide due to reactivation of latent virus.
  • The lack of a proven treatment to prevent fetal infection diminishes the benefit of universal screening.

When should a pregnant person be tested for CMV infection?

Per @mysmfm, screening should be reserved for clinical or ultrasound suspicion of maternal or fetal infection, meaning if the pregnant patient has clinical findings suspicious for CMV or there are certain findings on a fetal ultrasound, a maternal blood test can look for CMV antibodies. The results can help determine if you are already immune to CMV through infection in the past, or have had a recent exposure.

Even if these tests show you have had CMV infection in the past, it does not mean you are immune and there is no chance of fetal infection. As stated above, once exposed to CMV, the virus can remain latent in your system, become reactivated in pregnancy, and still cause fetal infection.The chance of fetal infection is highest if you have never had CMV infection in the past and you become infected for the first time during pregnancy.

Signs and symptoms of CMV infection

Many people will get CMV and be asymptomatic. If you do have signs, call your doctor immediately.

Symptoms include:

  • Fever
  • Sore throat
  • Fatigue
  • Swollen glands (lymphnodes)

People with weakened immune systems who get CMV can have more serious symptoms affecting the eyes, lungs, liver, esophagus, stomach, and intestines.

Understanding the risks of CMV during pregnancy to the fetus and infant

Per the CDC, “CMV is a common virus for people of all ages; however, a healthy person’s immune system usually keeps the virus from causing illness.”

  • The incidence of primary CMV infection (first-time infection) among pregnant persons ranges from 1% to 4%. In these pregnancies, 40% of fetuses will be infected, with 18% of infants being symptomatic at birth and 25% developing effects by age 2. Fetal infection rates are 30% in 1st trimester, 34–38% in 2nd trimester, and 40–72% in 3rd trimester. More serious fetal effects occur with infection in 1st trimester.
  • The incidence of severe fetal infection is much lower after recurrent infection. Of those pregnant persons with a history of CMV infection in the past, fetal infection will occur in 0.15–2%. Less than 1% of infants will be infected at birth, and 8% will have effects by age 2.

A recent study, showed that while rate of CMV vertical transmission increases over the duration of pregnancy, from 5% in the few weeks preceding conception to 60% in the third trimester. However, severe effects on the fetus much more likely is maternal infection occurs in the periconception period and first trimester (29% and 19%, respectively). After that, the risk of severe fetal effects is about 1%.

If CMV infection is suspected in the fetus, an amniocentesis will be recommended to confirm infection. If The results are positive for fetal CMV infection, there is no way to assess how severe the infection is or what the outcome for the baby will be.


Babies born with CMV can have brain, liver, spleen, lung, and growth problems. The most common long-term health problem in babies born with congenital CMV infection is hearing loss, which may be detected soon after birth or may develop later in childhood.

SMFM: CMV and Fetal Infection

Measures to prevent exposure

Childcare workers, families with young children, and some healthcare workers are at higher risk for infection. Measures to prevent infection include the following:

  • Use of gloves and rigorous hand washing after exposure to potentially infected articles, like diapers, or respiratory secretions
  • Avoidance of sharing utensils with or kissing young children if saliva is present.

Personal hygiene including hand washing is one of the best methods we have at reducing transmission of many illnesses including the common cold and flu, so never underestimate the power of proper hand washing! In addition, you can ask your physician about signs or symptoms to be mindful of for yourself and signs or symptoms in younger children. Though CMV is not something routinely screened for, it does not mean you cannot have a conversation with your physician about it so that you better understand it.


Is there a medication or vaccine available to prevent or treat CMV infection in pregnancy?

A CMV Vaccine…

A vaccine is not yet available, but according to the American College of Obstetrics and Gynecology (ACOG), development of a CMV vaccine for primary prevention has been the focus of several studies. Until a vaccine emerges, the best protection we have in reducing CMV is education on proper hygiene and transmission.

Hyperimmune globulin...

Studies on CMV hyperimmune globulin for the treatment of CMV infection in pregnancy have been inconclusive. Currently, this therapy is not recommended in pregnancy.


Learn more about a CMV vaccine trial

CMV Fact Sheet from the CDC

SMFM: CMV infection

CDC Fact Sheet
Shannon M. Clark, MD

Shannon M. Clark, MD

Shannon M. Clark, MD, MMS is a double board certified ObGyn and Maternal-Fetal Medicine Specialist, and founder of Babies After 35. In her roles as a clinician, educator and researcher at UTMB-Galveston, she focuses on the care of people with maternal and/or fetal complications of pregnancy. Dr. Clark has taken a special interest in pregnancy after the age of 35, which according to age alone, is considered a high-risk pregnancy.

Follow Shannon on TikTok @tiktokbabydoc, Facebook @babiesafter35, and Instagram @babiesafter35.

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