FAQ: What should clinicians know about congenital measles?

AAP added a congenital measles FAQ to Red Book Online, dated September 8, 2026, covering the definition, clinical presentation, evaluation and management, infection prevention and control, long-term follow-up, and prevention of the condition. The guidance was developed in response to ongoing measles outbreaks and the resulting increase in congenital measles cases in the United States.¹ AAP said it is addressing these questions as cases rise during the outbreaks, citing CDC data showing 3,134 U.S. measles cases among people of all ages this year, the most since 1991, and two deaths in Pennsylvania, including a newborn and 6-week-old baby.²

The recommendations differ based on when the birth parent's rash began relative to delivery, and the guidance also covers prepregnancy MMR vaccination, postexposure prophylaxis for susceptible pregnant persons, and separation and isolation decisions at birth.¹ Where evidence is available, the guidance cites it, but research is limited because case counts, especially in pregnant persons, have been low since measles was eliminated in the U.S. in 2000.² Where evidence is limited, the recommendations reflect the opinion of subject matter experts in infectious diseases, public health, infection prevention and control, and fetal and newborn medicine.^1,2

1. Why is measles during pregnancy a concern?

Measles during pregnancy can harm both the birth parent and the baby, and the most common fetal complications are pregnancy loss, premature delivery, and low birth weight. Infants who survive intrauterine and perinatal measles may also develop serious immunologic and neurologic complications months to years after infection. The guidance states that the available evidence does not support an association between measles in pregnancy and congenital defects.¹

Maternal measles in early pregnancy (for example, in the first or second trimester) can result in fetal exposure and potential complications such as miscarriage, stillbirth, and preterm delivery, but the clinical impact when the pregnancy continues is unclear because of limited data.¹

"Our goal is to help pediatricians care for newborns with congenital measles based on the existing evidence," said Lee Savio Beers, MD, FAAP, AAP chief medical officer. "While congenital measles was previously an uncommon condition and therefore the evidence is somewhat limited, this is an urgent need for pediatricians caring for patients in an active outbreak."²

2. What is congenital measles, and which neonates are considered exposed?

Congenital measles is defined as clinical and/or laboratory evidence of measles infection within the first 10 days of life in a neonate with intrauterine measles exposure, which occurs through transplacental transmission during maternal viremia. It differs from neonatal measles, in which exposure occurs after birth through close contact with an infectious person (horizontal transmission), and rash onset in a neonate more than 10 days after birth suggests postnatal exposure.¹

Historical studies suggest congenital measles was uncommon in the prevaccine era, when most pregnant women had been infected with measles in childhood. In the era of measles elimination, however, multiple case reports have documented congenital measles in neonates born to parents who were not immune before pregnancy and developed acute measles around delivery.¹

AAP advises that all neonates whose birth parent had measles during pregnancy, regardless of gestational age at maternal onset, be considered exposed. Infants born more than 14 days after maternal rash onset may have had acute infection in utero that resolved, but they remain at risk for delayed complications such as subacute sclerosing panencephalitis (SSPE). Management differs between neonates born during or shortly after acute maternal infection, defined as after prodromal symptom onset through 14 days after maternal rash onset, and those born more than 14 days after maternal rash onset.¹

"Many providers who have never seen measles except in textbooks are now having to learn what to do, how to look out for measles in their patients and how to manage them," said Pia S. Pannaraj, MD, MPH, FAAP, a member of the AAP Committee on Infectious Diseases and professor of pediatrics at the University of California, San Diego.²

3. How often is measles transmitted from the birth parent to the neonate?

Data on transmission rates are limited. Historical reports suggest vertical transmission occurs in approximately 25% to 30% of cases when maternal measles occurs in the days before birth.¹ ² During 2024 and 2025, one Canadian province reported 9 congenital measles cases among 51 confirmed measles infections that occurred during pregnancy.¹

The guidance also addresses the timing of transmission. Measles causes a low-level primary viremia shortly after exposure, during which people are asymptomatic, and vertical transmission generally occurs during the secondary high-level viremia associated with symptom onset. A neonate delivered shortly after documented exposure but before prodromal symptoms could theoretically have been exposed in utero, but no case reports suggest that primary viremia has resulted in vertical transmission.¹

4. How do infants with congenital measles present, and what outcomes should clinicians anticipate?

Presentation ranges from asymptomatic to the classic measles rash to fulminant, multisystem disease and death, with fever, rash, and jaundice the most common findings.¹ ² The classic maculopapular eruption may be atypical, delayed, or absent because of the infant's underdeveloped adaptive immune response, attenuation by passively acquired measles antibodies, or possibly other reasons, and additional manifestations may include thrombocytopenia, pneumonia, and neurologic complications.¹

Mortality attributable to congenital measles was reported to be up to 30% before the immune globulin era. Neonates with congenital measles are at increased risk of SSPE and may have a shorter latency (months to a few years) between acute infection and SSPE onset than older children.¹ AAP noted that serious consequences tend to occur more frequently and more quickly in congenital measles than in other cases.²

"Measles, especially in babies, is not just as simple as getting the rash and having it go away," Pannaraj said. "They can have multi-organ failure with rapid deterioration, or they may be completely asymptomatic at birth but have long-term consequences including severe secondary infections as well as heightened risk of down-the-road neurologic consequences."²

5. How should neonates be tested for measles?

Neonates born during or shortly after acute maternal infection, meaning after prodromal symptom onset through 14 days after maternal rash onset, should be tested. RT-PCR is suggested as the most sensitive and specific test and can be performed on respiratory specimens (nasopharyngeal or oropharyngeal/throat swab) and urine, with respiratory swabs preferred because of higher viral burden at those sites. RT-PCR testing of blood or birth products such as the placenta is limited to research settings.¹

Measles IgM testing can also be considered, since IgM is not passed vertically in utero and its detection in a neonate would suggest infection. Immune globulin intramuscular (IGIM) and immune globulin intravenous (IGIV) products are not expected to interfere with IgM testing because they do not contain substantial amounts of IgM, though false-positive and false-negative IgM results can occur.¹

A negative IgM or RT-PCR result in an asymptomatic neonate does not fully rule out in utero transmission, and negative results early after birth have in some instances been followed by positive results. Testing should be repeated if signs or symptoms develop during the monitoring period, and neonates with initial negative results who remain asymptomatic could be considered for repeat testing on day 10 of life. Among neonates with positive RT-PCR results, serial testing (for example, weekly) may be used to determine disposition and ongoing precautions in high-risk settings such as the NICU.¹

6. When should immune globulin and vitamin A be used?

AAP advises that all neonates born within 14 days of maternal rash onset be considered for immune globulin, which may prevent an overt, symptomatic congenital measles syndrome and limit morbidity and mortality in neonates who develop congenital measles.¹ ² For neonates without overt signs or symptoms, immune globulin should be given as soon as possible, and case reports suggest that IGIM or IGIV at or shortly after birth may attenuate or prevent symptoms. Immune globulin may also protect against postnatal acquisition if birth occurs during the maternal infectious period.¹

Management of symptomatic neonates is less clear. Immune globulin is expected to work best during the incubation period rather than during acute infection, but it has been given to some neonates with a measles exanthem at birth without noted adverse effects, and neonatal immune immaturity may mean it could help prevent morbidity.¹

IGIM is generally the preferred formulation for infants younger than 12 months who are exposed to measles, at a recommended dose of 0.5 mL/kg (maximum 15 mL). No specific guidance addresses the preferred route for neonates born to a parent with acute measles, and the choice between IGIM and IGIV may depend on product availability, intravenous access, and birth weight, which can affect the muscle mass available for injection.¹

Neonates with confirmed congenital measles, particularly those with overt symptoms, should receive vitamin A (50,000 IU [15,000 μg RAE], once daily for 2 days) as part of supportive management unless contraindicated, for example by severe liver disease. The role of vitamin A in neonates who test positive by RT-PCR but have no overt measles-like symptoms is unclear.¹

7. What isolation precautions apply when a neonate is born within 14 days of maternal rash onset?

Neonates of any gestational age born within 14 days of maternal rash onset should be delivered and managed in airborne isolation until neonatal infectiousness can be evaluated, to avoid unnecessary exposures. If the neonate has a measles exanthem or other symptoms suggestive of acute measles, airborne precautions should continue until the neonate is no longer considered infectious. For term neonates, the standard infectious period through 4 days after rash onset may be reasonable, but data are lacking and local circumstances may require longer isolation.¹

If the neonate is born within 14 days of maternal rash onset without an exanthem or suggestive symptoms, airborne precautions and symptom monitoring should continue through at least 14 days after maternal rash onset. If birth occurs during the maternal infectious period (from 4 days before through 4 days after rash onset), postnatal exposure is also possible, and precautions should be maintained for the standard 21 days after respiratory exposure. For neonates exposed postnatally, receipt of immune globulin would extend quarantine and monitoring to 28 days from birth.¹

Whether immune globulin extends the incubation period for vertically acquired measles is unknown, and the available literature suggests measles exanthems in neonates with congenital measles occurred within 8 days of maternal rash onset regardless of immune globulin receipt. For preterm neonates or those with congenital measles but no rash, the duration of airborne precautions may require case-by-case discussion with public health authorities, infection prevention specialists, and clinicians, since prolonged RT-PCR detection and potentially prolonged infectious periods have been reported, particularly in preterm neonates. Facilities could extend airborne isolation for the duration of illness, as recommended for immunocompromised patients, or, although data are lacking, discontinue isolation after 2 consecutive negative RT-PCR results. Household members who plan to visit should be carefully screened for measles exposure beforehand.¹

8. Should the birth parent and neonate be separated when the parent is infectious at delivery?

Data to guide separation decisions are limited. When a neonate is asymptomatic at birth during the maternal infectious period (from 4 days before through 4 days after rash onset), it may be unclear whether in utero transmission occurred, and postnatal transmission is possible and potentially avoidable. AAP advises weighing measles' high contagiousness and the potential for severe sequelae in consultation with the facility infection preventionist and the family. AAP recommends that parents with infections requiring airborne precautions avoid contact with the infant, but the infant can be fed the parent's expressed human milk. If the neonate is born after the maternal infectious period, no separation is recommended.¹

If the dyad is not separated during the infectious period, the parent should be in an airborne infection isolation room with 20 or more air changes per hour. The parent may consider source control, such as a NIOSH-approved disposable N95 respirator without an exhaust valve, although no data are available to inform this practice. Human milk remains a safe feeding option.¹

9. How should neonates born more than 14 days after maternal rash onset be managed?

Neonates born at or after 34 weeks' gestation more than 14 days after maternal rash onset are generally not expected to be at risk for a transmissible acute measles syndrome after birth. Congenital infection may have occurred in utero, but the neonate would not be expected to be infectious at birth, and transplacental passage of high levels of maternal IgG during convalescence should help suppress viral replication, unless a maternal condition such as uncontrolled HIV limits antibody transfer. Measles testing, isolation, and immune globulin may therefore not be required or beneficial.¹

Testing in this group is of unclear value, though some experts recommend testing asymptomatic neonates born after maternal measles at any point in pregnancy because of potential late complications and the infection control implications of detecting measles virus RNA. Immune globulin is usually not needed because the infant is beyond the window in which it would attenuate congenital infection, but it should be considered if the infant has a new exposure or the birth parent has a condition that prolongs viral shedding, such as uncontrolled HIV.¹

Empiric airborne precautions are recommended until measles testing is negative if the neonate is born preterm, is admitted to a setting with highly susceptible hosts such as the NICU or newborn nursery regardless of gestational age, or is born to a parent with conditions that limit placental antibody transfer. For delivery at or near term more than 14 days after maternal rash with rooming-in, standard precautions may be considered, and some infection preventionists may recommend airborne precautions regardless of setting.¹

AAP noted that IgG transfer before 32 weeks' gestation is more variable, with fetal concentrations reaching 50% of maternal concentrations by 32 to 34 weeks, so protection may be less reliable for neonates born very preterm. A case series of pregnant persons in France who developed measles more than 14 days before delivery found vertical transmission at the time of maternal infection: a neonate born at 40 weeks after maternal measles at 19 weeks tested RT-PCR positive in saliva, and a placental RT-PCR result was positive after delivery at 41 weeks following maternal measles at 33 weeks. Virus viability was not assessed, and no neonates in the series were symptomatic at birth.¹

10. How can measles in pregnancy be prevented, and what long-term follow-up is needed?

The best prevention is prepregnancy MMR vaccination to establish maternal immunity. Postexposure prophylaxis with IGIV is recommended for susceptible pregnant persons, and either IGIV or IGIM is recommended for exposed neonates.¹ Measles vaccines cannot be given during pregnancy because they contain live virus.²

"The best prevention is for people to get vaccinated before pregnancy, so they're protected," Pannaraj said.²

Neonates exposed to measles in utero at any gestational age may be at higher risk for delayed sequelae, including encephalitis and SSPE, than people infected later in life, and the latency may be short (months to a few years) with rapid neurologic onset. For infants and children with known congenital measles or known in utero exposure, AAP calls for long-term follow-up and vigilance for neurologic and immunologic complications, careful parental counseling, and monitoring for seizures, regression in milestones, and academic difficulties in older children, which might indicate early SSPE. No known interventions are proven to reduce poor neurologic outcomes, although antiviral and immunomodulatory treatments have been attempted.¹

References:

1. Congenital measles: frequently asked questions. Red Book Online. American Academy of Pediatrics. Published September 8, 2026. Accessed October 2, 2026. https://publications.aap.org/redbook/resources/35976

2. American Academy of Pediatrics. AAP addresses questions about congenital measles prevention, evaluation, management. Press release. Published September 8, 2026. Accessed October 2, 2026. https://publications.aap.org/aapnews/news/35977