A new health alert from the Pennsylvania Department of Health is warning doctors about congenital measles, a disease that was once extremely rare in the United States. But now that dozens of pregnant Pennsylvania women have contracted measles in the state’s ongoing outbreak, the potentially fatal infection passed from mother to baby in utero is poised to pose clinical challenges for physicians facing a disease they’ve never seen in practice.
So far, Pennsylvania has said 66 pregnant women have contracted measles while pregnant this year, and at least six babies in the state have been born with measles. Of the six deaths reported in the state, at least two have been in infants, but it’s not known if they had congenital infections.
Releasing information on infant outcomes in those pregnancies is illegal in Pennsylvania. According to NBC News, there is also no national database on congenital measles, likely because the disease hasn’t been routinely seen in the United States for decades.
No ‘denominator data’
“We don’t have denominator data on congenital measles,” said Adam J. Ratner, MD, MPH, a member of the American Academy of Pediatrics (AAP) Committee on Infectious Diseases, told CIDRAP News. The AAP released an updated FAQ on congenital measles last month.
Ratner explained that most of what is known about the disease comes from individual case studies and series. Because of this, it’s impossible to extrapolate how many pregnant women with measles will have an infant with congenital measles.
Furthermore, the case definition for congenital measles is tight: Only measles infections that occur in the last two weeks of pregnancy or the first 10 days post-delivery are considered congenital. But Ratner cited a 2021 case series in France described asymptomatic infants who tested positive for measles more than 20 weeks after maternal infection.
Another case series conducted during the large Canadian measles outbreak of 2025 described 51 pregnant women who contracted the virus, resulting in nine cases of congenital measles. One of the nine case-patients died.
There is definitely underreporting of prenatal measles, because mild cases of measles in pregnancy may not be picked up.
Compounding the denominator problem is reporting. “There is definitely underreporting of prenatal measles, because mild cases of measles in pregnancy may not be picked up,” Ratner said.
State urges MMR before pregnancy
In its alert, the Pennsylvania health department urges women to get the measles, mumps, rubella vaccine (MMR) before pregnancy. MMR is not recommended once pregnancy begins because it contains live virus.
If an unvaccinated pregnant woman is exposed to measles, she has a six-day window in which to take immunoglobulin therapies. If exposure happens to a pregnant women who received the two-dose MMR series in childhood, she should be well-protected against the virus.
“The presentation of congenital measles infection is highly variable, ranging from asymptomatic, to the classic measles rash, to fulminant, multisystem disease and death,” the state health department said. Treatment includes supportive care, and in the case of symptomatic infants, vitamin A, unless contraindicated. Asymptomatic infants born to mothers with active infections (rash onset within 14 days of birth) could also receive immunoglobulin.
As of yesterday, Pennsylvania reported 1,286 cases of measles, 109 of which were reported in the past week. The state’s dashboard lists five measles death, despite a sixth death reported earlier this month in Franklin County.
In an email to CIDRAP News, the Pennsylvania Department of Health said it was still investigating the Franklin County death and that the death would not be labeled “measles-associated” until there was evidence the death met all of the state’s criteria, including evidence of a measles infection and a positive laboratory test in the 30 days prior.