The essentials

Cytomegalovirus (CMV) is a very common herpes-family virus that stays dormant in the body for life. In healthy people it causes, at most, a mono-like illness that clears on its own. It matters in pregnancy, in babies infected before birth, and in people with a weakened immune system. Blood tests read IgG and IgM antibodies, IgG avidity and, when needed, viral DNA by PCR.

What is cytomegalovirus, at a glance?

  • Medical name: cytomegalovirus, or human herpesvirus 5, usually shortened to CMV[7]. It stays in the body for life, can reactivate, and a different strain can reinfect[1].
  • How common: in the United States, nearly 1 in 3 children is infected by age 5 and over half of adults by age 40[1]. Worldwide, about 83% of people carry CMV antibodies[8].
  • Congenital CMV: about 1 in 200 babies is born with it, and about 1 in 5 of those babies has birth defects or long-term health problems[2].
  • Key tests: CMV IgG and IgM, IgG avidity, and CMV DNA by PCR[3][6].

What are the symptoms of CMV?

Most people have no symptoms at all. When they do, they are usually mild: fever, sore throat, fatigue and swollen glands; occasionally CMV causes mononucleosis or hepatitis[1]. Muscle aches and a rash can also occur[5].

  • CMV mononucleosis: like Epstein-Barr mononucleosis, with fever, raised liver enzymes and atypical lymphocytes, but usually little sore throat and a negative "mono spot" test[7].
  • Recovery: most people recover in about 4 to 6 weeks without CMV-specific medicine[5].
  • Weakened immune system: reactivation can affect the lungs, gut, brain or, in advanced HIV, the retina[7].
  • Newborns with congenital CMV: rash, jaundice, a small head, low birth weight, seizures; hearing loss can appear later, even after a normal newborn hearing test[2].

When should I see a doctor about CMV?

When to see a doctor

  • Emergency: call 911 for sudden, severe pain in the upper left side of the belly, which can mean a ruptured spleen[5], or a newborn with a seizure.
  • Within 24 to 48 hours if you are pregnant and have a fever with a mono-like illness, or a positive CMV IgM result: the timing of the next test matters[10]. The same applies to fever or blurred vision after a transplant.
  • At your next appointment for an unexplained IgG or IgM result, or if your baby did not pass the newborn hearing screen.

How do you catch CMV, and who is at risk?

CMV spreads through body fluids: saliva, urine, blood, tears, semen and breast milk. It also passes through transplants, transfusions and from mother to baby[1].

  • Common A first infection in childhood or adolescence, often silent[1].
  • Common Parents of toddlers and childcare workers: exposure to young children is the main risk factor for a first infection in pregnancy, because infected children shed the virus in urine and saliva for a long time[10].
  • Possible Organ or stem cell transplantation, and advanced HIV infection (AIDS)[7].
  • Rare Complications in healthy people: Guillain-Barré syndrome, colitis, pneumonia or spleen rupture[5].

How is CMV diagnosed? Reading IgG, IgM and avidity

Testing is useful for a mono-like illness with a negative mono spot, in pregnancy, in newborns and around a transplant. Alongside CMV tests, a doctor may check a complete blood count, the platelet count and liver tests such as ALT[5].

How the two CMV antibody results are usually read (people older than 12 months)
CMV IgGCMV IgMUsual reading
NegativeNegativeNever infected ("seronegative")[3].
PositiveNegativePast infection, without saying when[3].
PositivePositivePossibly recent, but IgM also appears with reactivation and lasts months: avidity helps[3][10].
Negative, then positive on a second sampleAnyClear evidence of a recent first infection[3].

Our pages on IgG and IgM blood tests explain these antibody classes. CMV IgM persists in 50 to 80% of samples up to 6 months after a first infection, and false positives occur[10]. New IgG binds weakly (low avidity), then more strongly over 2 to 4 months[3]. A fictitious report from early pregnancy:

Fictitious example of a CMV serology report (United States format)
TestResultReference rangeFlag
CMV IgG antibody48.0 U/mLNegative: <6.0; positive: ≥6.0POS
CMV IgM antibody1.9 indexNegative: <0.85; equivocal: 0.85-0.99; positive: ≥1.00POS
CMV IgG avidity0.22 (low)Low: <0.50; intermediate: 0.50-0.60; high: >0.60L
  1. Units and cut-offs: each assay has its own units and limits; only those on your report apply.
  2. IgG positive: infection happened at some point[3].
  3. IgM positive: compatible with, not proof of, a recent infection[3].
  4. Low avidity: with a positive IgM, this is reliable evidence of a first infection within the last few months[3]. High avidity in the first trimester makes an early-pregnancy infection unlikely; intermediate values are retested[10]. US avidity tests are not FDA-approved[3].

IgG, IgM and avidity on the same report, each with its own units? BloodSense explains every line of your complete report in plain words and helps you prepare the questions to ask your doctor.

Explain my CMV test results

PCR (viral DNA): PCR measures the amount of virus (viral load). A negative PCR may miss very low levels[6], and CMV DNA in blood does not by itself prove disease[7]. See our guide to PCR results.

What does CMV mean in pregnancy?

A first (primary) CMV infection occurs in 1 to 2% of pregnancies, and the virus passes to the baby in about 32% of cases[10]. Serious long-term effects concern mainly first-trimester infections: about 23% of fetuses infected then have lasting problems[10]. Reactivation or reinfection can also reach the baby, with a similar impact[10].

  • Screening is debated. The 2024 European consensus recommends CMV serology as early as possible in the first trimester, repeated every 4 weeks until 14 to 16 weeks in women who test negative[10]. In the United States, the Society for Maternal-Fetal Medicine has not recommended routine screening of all pregnant women[11], nor did a 2017 international group[9].
  • Confirming a recent infection: by seroconversion, or by positive IgM with positive IgG and low avidity[11].
  • Is the baby infected? A PCR on amniotic fluid is reliable from 17 weeks, provided the amniocentesis is done at least 8 weeks after the mother's infection; a negative result is reassuring[10].
  • Treatment to lower transmission: after a primary infection around conception or in the first trimester, the European consensus recommends the antiviral valaciclovir, which lowers transmission by about 70%[10]. The 2016 US document limited antenatal treatment to research[11]: ask your obstetrician.

How is congenital CMV tested in newborns?

Antibody tests cannot diagnose congenital CMV[3]. The test is a PCR on saliva (more than 1 hour after breastfeeding), confirmed on urine, done within 3 weeks of birth; later, it cannot tell infection before birth from infection after[3][4]. Congenital CMV is also one of the infections behind some cases of cerebral palsy.

What follow-up tests are needed, and how often?

  • After a transplant: risk is judged before surgery from the CMV serostatus of donor (D) and recipient (R). For a kidney, D+/R− is high risk, R+ intermediate and D−/R− low[12]. Either preventive medicine is given for months, or blood CMV DNA is checked, weekly in high-risk patients, and treated when it rises[12].
  • Reading viral loads: results come in IU/mL, often as a log value; a change under 0.5 log (about 3-fold) may not be meaningful, so compare the same lab and sample type[12].
  • Children with congenital CMV: hearing checks until at least age 5 after a first-trimester or undated infection[10].
  • Healthy adults: your doctor decides whether raised liver enzymes need rechecking.

How is CMV treated?

No doses are given here: treatment is decided by your medical team.

  • Healthy people: usually no treatment beyond rest and symptom relief[1][5].
  • Weakened immune system: antivirals such as ganciclovir or valganciclovir, often with reduced immunosuppression after a transplant[7].
  • Newborns with significant symptoms: 6 months of antiviral treatment is recommended[10]; it may improve hearing but needs close monitoring[2].

How can I prevent CMV, especially in pregnancy?

  • Wash your hands with soap and water after diaper changes or toilet help[2].
  • Do not share food, utensils, cups or pacifiers with young children, and avoid contact with their saliva and urine[2].
  • Start these habits before conception and keep them through the first trimester, when they matter most[10].
  • No CMV vaccine is licensed; candidates are still in clinical trials[10].

Questions to ask your doctor

  1. Do my IgG and IgM results mean a past infection, a recent one or a reactivation?
  2. Is an IgG avidity test needed, and which laboratory performs it?
  3. If I am pregnant: what is the likely timing of the infection, and is an amniocentesis or treatment worth discussing?
  4. After my transplant: how often will my CMV viral load be checked, and what change would trigger treatment?

Frequently asked questions

Is CMV the same as mononucleosis?

No. Classic mono is caused by the Epstein-Barr virus. CMV can cause a very similar illness, but the mono spot test is negative and CMV serology is positive[7].

Is CMV a sexually transmitted infection?

It can spread sexually, but also through saliva, urine and breast milk[1].

Does a positive CMV IgG protect me during pregnancy?

It lowers the risk but does not remove it: a reinfection or reactivation can still reach the baby, and a positive IgG cannot rule out fetal infection[10].

How is CMV different from toxoplasmosis on a pregnancy test panel?

Both are read with IgG, IgM and avidity, but they are different germs with different sources: toxoplasmosis comes mainly from undercooked meat and cat litter. See our page on the toxoplasmosis blood test.

  1. Centers for Disease Control and Prevention. About cytomegalovirus. January 17, 2025. cdc.gov (accessed October 26, 2026)
  2. Centers for Disease Control and Prevention. About congenital CMV. January 17, 2025. cdc.gov (accessed October 26, 2026)
  3. Centers for Disease Control and Prevention. Laboratory testing for CMV and congenital CMV. April 15, 2024. cdc.gov (accessed October 26, 2026)
  4. Centers for Disease Control and Prevention. Clinical overview of CMV and congenital CMV. November 6, 2024. cdc.gov (accessed October 26, 2026)
  5. MedlinePlus Medical Encyclopedia. Cytomegalovirus (CMV) infection. Reviewed August 29, 2024. US National Library of Medicine. medlineplus.gov (accessed October 26, 2026)
  6. MedlinePlus. Cytomegalovirus (CMV) tests. Updated September 9, 2026. US National Library of Medicine. medlineplus.gov (accessed October 26, 2026)
  7. MSD Manual Professional Version. Cytomegalovirus (CMV) infection. Reviewed January 2026. merckmanuals.com (accessed October 26, 2026)
  8. Zuhair M, Smit GSA, Wallis G, et al. Estimation of the worldwide seroprevalence of cytomegalovirus: a systematic review and meta-analysis. Rev Med Virol. 2019;29(3):e2034. doi:10.1002/rmv.2034 (accessed October 26, 2026)
  9. Rawlinson WD, Boppana SB, Fowler KB, et al. Congenital cytomegalovirus infection in pregnancy and the neonate: consensus recommendations for prevention, diagnosis, and therapy. Lancet Infect Dis. 2017;17(6):e177-e188. doi:10.1016/S1473-3099(17)30143-3 (accessed October 26, 2026)
  10. Leruez-Ville M, Chatzakis C, Lilleri D, et al. Consensus recommendation for prenatal, neonatal and postnatal management of congenital cytomegalovirus infection from the European congenital infection initiative (ECCI). Lancet Reg Health Eur. 2024;40:100892. doi:10.1016/j.lanepe.2024.100892 (accessed October 26, 2026)
  11. Society for Maternal-Fetal Medicine. Diagnosis and antenatal management of congenital cytomegalovirus infection. Am J Obstet Gynecol. 2016;214(6):B5-B11. doi:10.1016/j.ajog.2016.02.042 (accessed October 26, 2026)
  12. Kotton CN, Kumar D, Manuel O, et al. The fourth international consensus guidelines on the management of cytomegalovirus in solid organ transplantation. Transplantation. 2025;109(7):1066-1110. doi:10.1097/TP.0000000000005374 (accessed October 26, 2026)

This page is general information. It does not replace the advice of a doctor, who interprets your results with your symptoms, history, pregnancy stage and examination.