Maternal primary and non-primary infection (exogenous reinfection with a different strain or endogenous viral reactivation) of cytomegalovirus (CMV) during pregnancy can result in in utero transmission to the fetus (1). Infants can be categorized as symptomatic or asymptomatic based on clinical symptoms/signs (Table 1) (2). Approximately 11% of live-born infants born with congenital CMV (cCMV) have abnormal clinical findings at birth (symptomatic) (3). Infants can experience substantial morbidity, mortality, and long-term sequelae, including sensorineural hearing loss (SNHL), the most common sequela (4, 5). Infants without symptoms at birth are also reported to be at risk of developing long-term hearing loss (6). As a leading cause of congenital infections worldwide (7), cCMV infection meets many of the criteria for screening: it is clinically important, well defined and prevalent (4). Nevertheless, neither universal antenatal screening for CMV during pregnancy nor universal neonatal screening is routinely recommended (8) and there remain several challenges that impede their implementation. Roche Centralised and Point of Care Solutions and Roche Molecular Diagnostics convened a group of CMV experts (microbiologists, virologists, and clinicians) to discuss and offer strategies to address these barriers and knowledge gaps. This paper provides an overview of those discussions and is a narrative review of serologic and viral nucleic acid screening and diagnostics in the context of maternal, fetal and neonatal CMV infection.

CMV screening is offered to some pregnant women in parts of Europe, Israel, Australia and the USA in the setting of population-based studies, and independently of nationally endorsed screening programs (9). However, universal antenatal screening for CMV is not routinely recommended (8). Reasons not to screen include the absence of medication to prevent transmission and the difficulty of predicting sequelae (10).

The introduction of routine testing for CMV in pregnant women has several implications. Despite the difficulties mentioned above, the most important benefit of screening would be to identify fetuses at risk of developing sequelae.

Maternal screening, ideally early in the first trimester, would also identify those who were CMV-seronegative and thus allow information to be provided regarding hygiene and behavioral measures to prevent CMV infection. Evidence has shown that intervention based on the identification and hygiene counseling of CMV-seronegative pregnant women significantly prevents maternal infection (11). Hygiene counseling may also provide (as yet unproven) benefits for those who are seropositive.

During early pregnancy, repeat serologic screening with CMV-specific immunoglobulin G (IgG) and -M (IgM) antibodies of previously seronegative pregnant women at the end of the first trimester (or until week 20) would identify maternal primary CMV infection. Although there are no universally accepted guidelines, testing before 18–20 weeks of pregnancy is reasonable in order to identify late seroconversion at the end of the first trimester and implement fetal investigations. In the event of seroconversion, parents should be informed of the risk of vertical transmission [32% (3)] and the possible consequences.

Other strategies that could be put in place include maternal screening at the first prenatal visit and at birth, and neonatal screening at birth for those whose mothers tested seropositive, with diagnosis of the neonate by saliva or urine CMV DNA detection. Previously, this approach to targeted testing detected 82% of all cCMV infections (12). Notably, this study utilized culture for diagnosis; the detection rate is likely to be improved with polymerase chain reaction (PCR). This approach may be more cost-effective than screening all children.

However, screening tests do not identify which mothers will transmit the virus (13). Moreover, there are no surrogate markers to predict whether infection in the infant will lead to long-term sequelae.

Lastly, there are also risks for the mother associated with maternal screening for CMV that include the stress of having extra tests, the potential for unnecessary terminations (14), the potential risk of miscarriage or stillbirth from confirmatory amniocentesis [inversely correlated to skill/experience of operator (15)], and the cost. The challenge is in providing women with choice and information in the context of population-based economics.

Neonatal CMV screening would enable early detection of cCMV (following primary and non-primary maternal infection), but universal neonatal screening for CMV is currently not recommended by any public health body. Data from Uematsu and colleagues emphasize that without neonatal screening some infected neonates that develop neurological sequelae may go unrecognized (39).

Although universal screening is not performed, targeted screening of newborns who fail the neonatal hearing test has been implemented in some hospitals and states in the USA (40, 41). In the UK, Belgium and Australia, targeted testing of infants who were referred for further audiological testing (after failing the routine hearing screening) has also been trialed with some success (42–44). This combination of targeted newborn screening and early detection and interventions is likely to benefit children with cCMV (45).

Additionally, the costs associated with targeted neonatal screening look favorable compared with other screening programs (46, 47). However, this targeted approach would miss those CMV-positive infants who pass the newborn hearing test but are still at risk for late-onset SNHL (40, 48). In one study, 43% of infants with CMV-related SNHL in the neonatal period and cCMV infants who are at risk for late-onset SNHL were not identified by newborn hearing screening (49).

There are risks associated with neonatal screening, such as the potential for parental anxiety while waiting for confirmatory testing results. In addition, there may be anxiety related to the extended period of audiological monitoring that a cCMV-positive infant must undergo [up to 6 years (2, 50, 51)]. Most cCMV infections are asymptomatic and do not present a risk for the onset of late sequelae (5). Recent data demonstrated that primary maternal infections before the 14th week of pregnancy, the presence of a disseminated infection at birth, and imaging abnormalities in the neonate were risk factors for SNHL (52). This is a step toward the development of neonatal predictive markers that can be used to identify those at high risk of developing sequelae.

Although significant advancements have been made, many questions remain unanswered in this field (Table 2). Well-designed clinical trials to address several facets of CMV treatment (in pregnant women, CMV-infected fetuses and both symptomatic and asymptomatic neonates and children) are required. Prevention (vaccines), biology, and transmission factors associated with non-primary CMV, and the cost-effectiveness of universal screening, all demand further exploration to fully realize the ultimate goal of preventing cCMV.

Currently, treatment with immunoglobulins or antiviral therapy to prevent intrauterine transmission of CMV in pregnant women with primary CMV infection is not recommended as studies have not yet conclusively shown a benefit (63–66). Data from a non-randomized study showed that biweekly administration of hyperimmunoglobulin until 20 weeks' gestation successfully prevented maternal-fetal transmission of primary infections (65). These data need to be confirmed by a randomized clinical trial (67); if the results are confirmed, two-weekly intervals for testing seronegative women would be necessary. It has been suggested that a study that demonstrates treatment efficacy resulting in at least a 47% reduction in cCMV disease would make universal screening and treating for primary CMV in pregnancy cost-effective (10).

Whilst recent improvements in screening and diagnosis allow detection of primary CMV infection in pregnancy, unfortunately treatment options for CMV-infected fetuses and neonates are limited due to insufficient evidence for safety and effectiveness. Consequently, routine antiviral therapy to treat fetal CMV during pregnancy is not recommended (9). In infants with clinical disease at birth, early intervention with ganciclovir or valganciclovir can prevent hearing deterioration and improve developmental outcomes, although both treatments are associated with neutropenia (68, 69) and other possible long-term effects (70). Currently, valganciclovir treatment is recommended based on severity or number of symptoms. A European expert consensus statement recommends that treatment with oral valganciclovir (intravenous ganciclovir under certain circumstances) is only for those with: evidence of central nervous system disease; evidence of life-threatening disease, severe single-organ disease or multi-organ involvement; “moderate” cCMV disease once discussed on a case-by-case basis with a clinician with experience of managing infants with cCMV (2). The informal International Congenital Cytomegalovirus Recommendations Group recommend oral valganciclovir treatment for those neonates with “moderately” to “severely” symptomatic cCMV disease (9). Further development of efficacious antivirals with an acceptable safety profile is required.

Letermovir is a new agent approved for use in the prophylaxis of CMV infection in CMV-seropositive recipients of an allogeneic hematopoietic stem cell transplant over the age of 18 years (71). A recent case study revealed potential efficacy in pediatric allogeneic hematopoietic stem cell transplant patients (72). Further studies are required to determine whether it is safe and effective for treating those with cCMV.

More asymptomatic infants will be discovered if screening programs become widespread. Currently, antiviral therapy for asymptomatic infants is not recommended (2) but, like symptomatic infants, they are at risk of developing late-onset sequelae (53). Trials that investigate which interventions are effective and safe for asymptomatic infants or those with isolated hearing loss or subtle neuroimaging abnormalities, as well as older children that develop late-onset hearing loss, are necessary. Since clinical trials are ongoing (73–75), some of these points will hopefully be clarified in the next few years and the best management plan for this population determined.

As well as trials targeting treatment for specific populations, data on prevention are also required. It is known that natural infection confers some protection against both horizontal and vertical transmission (13, 76), therefore the development of an effective vaccine is feasible. Clinical trials of CMV vaccines should evaluate protection against cCMV infection (77). Recent modeling data of a single fictional cohort of 390,000 adolescent women suggest that vaccination could be cost-effective (78).

In the absence of a vaccine to prevent infection, a greater focus on education and prevention strategies for cCMV infection are needed for women intending to become pregnant, those already pregnant, and healthcare professionals alike. Preconception screening in those attending a fertility clinic, with resultant counseling to improve personal hygiene in those who were not immune to CMV, has shown that hygiene counseling (albeit in this highly selected cohort) is effective in reducing CMV exposure (79). In pregnant women, hygiene counseling of CMV-seronegative pregnant women significantly prevents maternal infection (11). De Vries and colleagues showed that non-primary infections account for the majority of CMV-related hearing loss, suggesting prevention research should encompass all pregnant women, not just those who are seronegative (80). Therefore, the current method aimed at preventing transmission of CMV—education concerning hygiene measures to be taken around small children [such as avoiding kissing babies on the mouth, not sharing cutlery with young children, and hand hygiene after a diaper change (11)]—should be performed regardless of knowing the mother's serostatus. However, in the general population, there is inadequate evidence to show that education translates into a decrease in maternal infection (4). Studies assessing the efficacy of hygiene measures on the prevention of CMV infection in pregnancy, and resultant cCMV, are necessary in women of reproductive age and are ongoing in the UK (81).

Clinicians do not know whether a non-primary infection is a reactivation or an infection with another strain of CMV. This distinction may be important in understanding the etiology of CMV disease, thus more research on the role of non-primary maternal CMV infections in congenital infection is necessary. At present, there are no tools validated to identify women at risk of transmitting the virus after a non-primary infection.

Finally, further evidence of cost-effectiveness is required. Whilst the cost-effectiveness of universal and targeted newborn cCMV screening programs has been assessed in the UK and USA (46, 47), and the economic burden of cCMV in the UK estimated (82), currently there are insufficient cost-benefit data, which hinders the implementation of screening.

cCMV infection results in significant consequences for the infected neonate. Despite this, universal maternal or neonatal screening for CMV and cCMV is not routinely recommended. A summary of our current recommendations for diagnosis, screening, and prevention is provided in Table 3. Presently there are significant gaps in understanding that prevent the implementation of universal screening, including insufficient data on cost-effectiveness and the lack of evidence for safe and efficacious treatments for those infected. Additionally, further data on non-primary maternal infection and the risk of cCMV infection are necessary. In the near future, we are confident that many aspects related to diagnosis, maternal and fetal therapy, and active prevention will surely present an improvement and our recommendations may change. Until then, and in the absence of a vaccine, hygiene recommendations to prevent CMV infection should be made to all pregnant women.

TL and ML-V wrote the first draft of the manuscript. All authors (TL, DB-G, M-LD, IF, SL, SM, and ML-V) contributed to manuscript revision, read and approved the submitted version.