Cytomegalovirus is one of the most common infections in the world. By adulthood, the majority of people have been exposed to it, often without ever knowing. For most healthy individuals, CMV causes no lasting harm — the immune system manages it quietly, and life continues without disruption.
During pregnancy, however, the picture changes. When a woman experiences a primary CMV infection for the first time while pregnant, or in some cases when a prior infection reactivates, the virus can cross the placenta and reach the developing fetus. This is congenital CMV — and it is the leading infectious cause of birth defects and childhood hearing loss in the United States, affecting approximately one in every 200 newborns, according to the Centers for Disease Control and Prevention (CDC).
Despite this prevalence, awareness of congenital CMV remains remarkably low. The National CMV Foundation has found that the vast majority of women have never heard of cCMV before or during pregnancy — a gap in health literacy that has real consequences for detection, monitoring, and early support for affected children.
National Congenital CMV Awareness Month, observed each June, exists to close that gap. Understanding the biomarkers associated with CMV infection — what they measure, what they indicate, and how they are used in both maternal and newborn contexts — is a foundational part of that understanding.
What Congenital CMV Actually Is
Cytomegalovirus (CMV) belongs to the herpesvirus family, the same group that includes the viruses responsible for chickenpox and infectious mononucleosis. Like other herpesviruses, CMV establishes lifelong latency after initial infection — remaining dormant in the body and occasionally reactivating, particularly when the immune system is under stress.
CMV spreads primarily through close contact with infected bodily fluids, including saliva, urine, breast milk, blood, and genital secretions. Young children — particularly those in group care settings — are among the most common sources of transmission to pregnant women, as toddlers frequently shed the virus in saliva and urine at high levels and for extended periods without any visible illness.
How CMV Is Transmitted During Pregnancy
The risk of the virus reaching the developing fetus depends significantly on the type of maternal infection. A primary infection — meaning the mother contracts CMV for the first time during pregnancy — carries the highest risk of fetal transmission, estimated at 30–40%. When transmission does occur following a primary infection, the risk of the newborn having symptoms or long-term effects is also highest.
Non-primary infections — meaning reactivation of a previous CMV infection or reinfection with a different CMV strain — can also result in fetal transmission, though at lower rates and generally with a lower probability of significant fetal impact. Women who had CMV before pregnancy retain some immune protection, but this does not entirely eliminate transmission risk.
Once the virus crosses the placenta, it can infect fetal cells, interfering with normal development — particularly of the brain and sensory systems. The timing of maternal infection during pregnancy is relevant: infections occurring earlier in the first trimester are generally associated with a higher risk of significant fetal effects.
Why Many Cases Are Asymptomatic at Birth
One of the most clinically significant and widely underappreciated aspects of congenital CMV is that the majority of infected newborns appear entirely healthy at birth. Approximately 90% of cCMV-affected babies are born without visible signs of infection — a condition described as asymptomatic cCMV.
This does not mean the infection has no consequences. Among babies born with asymptomatic cCMV, an estimated 10–15% will develop hearing loss or other neurological complications over the months and years that follow — sometimes not becoming apparent until a child is a toddler or school-aged. Without awareness of cCMV and a confirmed diagnosis, the cause of this hearing loss may go unidentified, delaying access to intervention and support.
Why cCMV Awareness Month Matters
The Impact on Hearing and Development
Sensorineural hearing loss — damage to the inner ear or auditory nerve — is the most common consequence of congenital CMV. The CDC estimates that cCMV causes more cases of childhood hearing loss each year than all other well-known causes combined, including Down syndrome, spina bifida, and neonatal herpes. In some affected children, hearing loss is present at birth and identified through standard newborn hearing screening. In others, it develops or progresses after birth, which is why ongoing audiological monitoring is an important part of cCMV follow-up care.
Beyond hearing, cCMV can be associated with a range of developmental outcomes in more severely affected infants, including cognitive and motor delays, vision impairment, and epilepsy. For the children most affected — those born with symptomatic cCMV — early identification opens the door to antiviral treatment, early intervention services, and specialised support that can meaningfully improve developmental trajectories.
Who Is at Higher Risk?
Pregnant women who have not previously been infected with CMV — meaning they are seronegative, without prior antibody protection — face the highest risk from a new primary infection during pregnancy. Women who work closely with young children, including those in childcare, early childhood education, or paediatric healthcare settings, have elevated daily exposure risk due to the high rates of CMV shedding in toddlers.
Mothers with young children already at home also face increased exposure risk. A toddler attending daycare has a meaningfully elevated chance of CMV acquisition, and within family settings, hand-to-mouth contact, shared utensils, and kissing are common transmission routes.
Immunocompromised individuals face a distinct category of CMV risk — though this article focuses specifically on maternal and congenital infection in the context of otherwise healthy pregnancies.
Key Biomarkers Linked to CMV Infection
Understanding which biomarkers are relevant to CMV — and what each one actually measures — helps pregnant women and new parents engage more meaningfully with screening results and clinical conversations.
CMV IgG and IgM — Understanding Maternal Antibodies
The two primary antibody markers used in maternal CMV screening are immunoglobulin G (IgG) and immunoglobulin M (IgM).
CMV IgG indicates prior exposure to cytomegalovirus. When someone has been infected with CMV at any point in their life — months or years ago — their immune system retains IgG antibodies directed against it. A positive CMV IgG result in a pregnant woman means she has had CMV before. This is sometimes described as seropositive status. Women who are IgG-positive before pregnancy carry some degree of immune memory, which reduces but does not eliminate the risk of reactivation or reinfection affecting the fetus.
A negative CMV IgG result means the woman has not previously encountered CMV and has no existing immunity. This seronegative status is the higher-risk scenario, as any new CMV exposure during pregnancy would represent a primary infection with the associated higher transmission risk.
CMV IgM indicates more recent immune activity. IgM antibodies are typically produced in the early stages of an immune response, rising within the first weeks of infection and generally declining over several months. A positive CMV IgM result can suggest recent or active infection — but IgM interpretation requires care. False-positive IgM results occur, and IgM can sometimes remain detectable for longer than expected. IgM positivity alone does not confirm that an infection occurred during the current pregnancy, nor does it confirm fetal transmission.
The combination of IgG and IgM results is interpreted together — and in many cases, a further test is needed to clarify the picture.
IgG Avidity — Identifying Recent Infection
When both CMV IgG and IgM are positive, the clinical question becomes: did this primary infection happen recently, or has it been present for longer? The answer matters significantly for understanding fetal risk.
IgG avidity testing helps answer this question. Avidity refers to the strength of the binding between an antibody and its target antigen. Early in an infection, IgG antibodies bind relatively weakly — low avidity. Over the following months, the immune system refines its antibody response, producing IgG with progressively stronger binding — high avidity.
A low avidity result suggests that the IgG antibodies are recently formed, indicating that the primary infection likely occurred within the past three to four months. This is the timing most relevant to fetal transmission risk. A high avidity result suggests that the infection was more distant in time — typically more than three months prior — providing some reassurance that the primary infection may have predated the pregnancy or occurred early enough that the highest-risk window has passed.
IgG avidity is a nuanced test that requires experienced laboratory interpretation and clinical context. It is most useful when ordered in conjunction with IgG and IgM results and reviewed by an obstetrician or maternal-fetal medicine specialist.
PCR Testing — Confirming Active Infection in Newborns
For newborns, the central question is different: not whether exposure occurred, but whether the virus is actively present in the baby. This is where polymerase chain reaction (PCR) testing plays its defining role.
PCR is a molecular technique that detects the genetic material of a virus directly — in this case, CMV DNA. For newborn cCMV diagnosis, the most common and practical samples are saliva and urine, both of which are non-invasive and easy to collect. A positive PCR result from saliva or urine collected within the first three weeks of life is considered the reference standard for confirming congenital CMV — meaning the virus was acquired before birth rather than after.
The three-week window is critical. CMV can also be acquired after birth through breast milk or other postnatal exposure, and infection acquired after birth does not carry the same developmental implications as congenital infection. If PCR testing is performed after three weeks, it becomes impossible to definitively distinguish congenital from postnatal acquisition.
Quantitative CMV viral load — a PCR test that measures the concentration of CMV DNA in the blood — is used in clinical settings to monitor infection activity in confirmed cCMV cases, particularly in newborns receiving antiviral treatment. Higher viral loads in blood at birth have been associated with more significant clinical findings, though individual outcomes vary and viral load alone does not predict prognosis.
What CMV Biomarkers Can (and Cannot) Tell You
Exposure vs. Active Infection
A theme central to CMV biomarker literacy is the distinction between exposure and active infection. A positive CMV IgG result means the immune system has encountered CMV — it does not mean CMV is currently active or that it poses an ongoing risk. In the vast majority of IgG-positive adults, CMV is latent and clinically silent.
A positive CMV IgM result suggests more recent immune activity, but requires careful interpretation — it does not independently confirm a clinically significant current infection, particularly in the absence of symptoms.
PCR testing, by contrast, detects active viral presence directly. A positive PCR result from a newborn saliva or urine sample within the first three weeks of life is the most definitive signal available for confirming congenital infection.
These distinctions matter because the appropriate next steps — clinical monitoring, specialist referral, antiviral consideration — depend on understanding which kind of positive result has been identified.
The Importance of Timing in Testing
CMV testing is particularly sensitive to timing in ways that differ from many other biomarker contexts. For maternal IgG avidity testing, the result’s clinical meaning depends on when in pregnancy testing occurs and when the IgM became positive. For newborn PCR, the diagnostic window closes at three weeks of age.
These timing dependencies underscore why CMV biomarker results are most informative when discussed with an obstetrician, maternal-fetal medicine specialist, or paediatrician who can incorporate gestational age, symptom history, and clinical context into their interpretation.
Who May Benefit From CMV Screening
Pregnant Women Without Prior Immunity
Women who do not know their CMV status — and particularly those in occupational or household settings with high toddler exposure — may benefit from discussing CMV IgG screening with their healthcare provider early in pregnancy. Knowing one’s serostatus supports more informed hygiene practices for seronegative women (such as avoiding sharing utensils, cups, or kissing toddlers on the mouth) and can guide closer clinical monitoring if seroconversion is suspected during pregnancy.
Some countries include CMV screening as part of routine prenatal panels; others do not. In the United States, universal prenatal CMV screening is not currently standard practice, though it is available on request and is increasingly discussed in high-risk settings. Awareness of this option is itself a meaningful step.
Families With Multiple Young Children
Households with toddlers or young children in daycare represent a real-world elevated exposure environment for pregnant women. A toddler shedding CMV in saliva and urine — entirely asymptomatically — is a common source of primary maternal infection. For women in this situation who are either currently pregnant or planning pregnancy, a conversation with their obstetrician about CMV serostatus and hygiene guidance is particularly relevant.
Newborns With Failed Hearing Screens
All newborns in the United States receive hearing screening before discharge from hospital. When a baby does not pass the initial screen, follow-up testing is arranged. In some cases, hearing loss is identified — and the cause may not immediately be clear. CMV is among the most important possibilities to investigate in this context.
Current guidance from the National CMV Foundation and various professional organisations supports targeted CMV PCR testing for newborns who fail their hearing screen, since a confirmed cCMV diagnosis would influence both monitoring and management decisions. Parents of a baby who did not pass their newborn hearing screen and have questions about cCMV should discuss PCR testing timing and availability with their paediatrician as promptly as possible.
Taking Ownership of Maternal and Newborn Health Data
How Direct-to-Consumer CMV Antibody Testing Works
CMV IgG and IgM antibody testing is available through direct-to-consumer lab testing platforms. After selecting a CMV antibody test, a blood sample is collected at a certified local laboratory and results are delivered through a secure digital platform, typically within a few days.
For women who are pregnant or planning pregnancy and have not previously been tested, DTC testing can provide an accessible first step toward understanding CMV serostatus. A positive IgG result provides reassurance of prior immunity and an indication of seropositive status. A negative IgG result identifies seronegative status — the scenario in which primary infection during pregnancy would carry the highest fetal transmission risk — and makes a conversation with an obstetrician about hygiene precautions and clinical monitoring particularly relevant.
IgM results from a DTC screen require clinical follow-up to interpret properly. A positive IgM result should be discussed with a healthcare provider, who may recommend IgG avidity testing and further obstetric evaluation. DTC testing for CMV antibodies is a starting point for awareness — not a clinical assessment in itself.
Newborn PCR testing, which involves saliva or urine collection and must be performed within the critical first three weeks of life, is a clinical procedure conducted through paediatric or hospital-based care, not a DTC service. Parents with questions about newborn CMV PCR should speak with their paediatrician promptly, particularly if their newborn did not pass a hearing screen.
Monitoring Viral Load and Hearing Over Time
For families navigating a confirmed cCMV diagnosis, monitoring does not end with the initial confirmation. Newborns with confirmed cCMV — whether symptomatic or asymptomatic — typically receive structured audiological follow-up to monitor hearing at regular intervals, since cCMV-related hearing loss can fluctuate and sometimes progress in the first years of life.
In clinical settings, quantitative CMV viral load in blood is monitored in infants receiving antiviral treatment, providing data that helps guide clinical decision-making. Serial audiological assessments, developmental evaluations, and — where indicated — brain imaging form part of the longitudinal monitoring approach for affected infants.
For parents engaged in this monitoring process, understanding what each marker measures — and what changes in it may signal — supports more informed participation in their child’s care team conversations.
The Role of Awareness Campaigns in Early Identification
Congenital CMV is sometimes called “the great imitator” of other newborn conditions — its symptoms, when present, can resemble those of other infections, and its most common consequence, progressive hearing loss, develops quietly in a child who seemed entirely healthy at birth. This is why awareness campaigns have a specific, urgent purpose: to put the name “congenital CMV” into the vocabulary of pregnant women, parents, and healthcare providers before a situation arises that requires it.
The research is clear that earlier identification of cCMV-affected infants — within the newborn period — creates more options for monitoring, antiviral treatment in eligible cases, and early intervention services. Hearing loss identified earlier leads to earlier audiological support, earlier fitting of hearing devices where needed, and earlier access to language and developmental programmes that can make a significant difference in outcomes.
This June, if you are pregnant, planning to become pregnant, or are a new parent, consider making CMV part of your health literacy. Ask your obstetrician about your CMV serostatus. If you have a toddler at home and are pregnant, understand the hygiene practices associated with reduced transmission risk. If your newborn did not pass their hearing screen, ask specifically whether CMV PCR testing has been considered and, if so, move quickly — the three-week window matters.
Awareness is not just a month. It is the foundation of every informed decision that follows.
This article is for educational purposes only and does not constitute medical advice. CMV antibody results and newborn PCR findings require clinical interpretation by a qualified healthcare provider. Newborn PCR testing for congenital CMV must be performed within the first three weeks of life to be diagnostically meaningful — parents with concerns should contact their paediatrician promptly. Direct-to-consumer testing is a health awareness tool and does not diagnose, treat, or prevent any medical condition.
