Reports of three neonates with elevated IgM antibody concentrations whose mothers had COVID-19 in two articles raise questions about whether the infants may have been infected with the virus in utero.
The data, while provocative, “are not conclusive and do not prove in utero transmission” of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), editorialists cautioned.
“The suggestion of in utero transmission rests on IgM detection in these 3 neonates, and IgM is a challenging way to diagnose many congenital infections,” David W. Kimberlin, MD, and Sergio Stagno, MD, of the division of pediatric infectious diseases at University of Alabama at Birmingham, wrote in their editorial. “IgM antibodies are too large to cross the placenta and so detection in a newborn reasonably could be assumed to reflect fetal production following in utero infection. However, most congenital infections are not diagnosed based on IgM detection because IgM assays can be prone to false-positive and false-negative results, along with cross-reactivity and testing challenges.”
None of the three infants had a positive reverse transcriptase–polymerase chain reaction (RT-PCR) test result, “so there is not virologic evidence for congenital infection in these cases to support the serologic suggestion of in utero transmission,” the editorialists noted.
Examining the possibility of vertical transmission
A prior case series of nine pregnant women found no transmission of the virus from mother to child, but the question of in utero transmission is not settled, said Lan Dong, MD, of the department of obstetrics and gynecology at Renmin Hospital of Wuhan University in China and colleagues. In their research letter, the investigators described a newborn with elevated IgM antibodies to novel coronavirus 2019 born to a mother with COVID-19. The infant was delivered by cesarean section February 22, 2020, at Renmin Hospital in a negative-pressure isolation room.
“The mother wore an N95 mask and did not hold the infant,” the researchers said. “The neonate had no symptoms and was immediately quarantined in the neonatal intensive care unit. At 2 hours of age, the SARS-CoV-2 IgG level was 140.32 AU/mL and the IgM level was 45.83 AU/mL.” Although the infant may have been infected at delivery, IgM antibodies usually take days to appear, Dr. Dong and colleagues wrote. “The infant’s repeatedly negative RT-PCR test results on nasopharyngeal swabs are difficult to explain, although these tests are not always positive with infection. … Additional examination of maternal and newborn samples should be done to confirm this preliminary observation.”
A review of infants’ serologic characteristics
Hui Zeng, MD, of the department of laboratory medicine at Zhongnan Hospital of Wuhan University in China and colleagues retrospectively reviewed clinical records and laboratory results for six pregnant women with COVID-19, according to a study in JAMA. The women had mild clinical manifestations and were admitted to Zhongnan Hospital between February 16 and March 6. “All had cesarean deliveries in their third trimester in negative pressure isolation rooms,” the investigators said. “All mothers wore masks, and all medical staff wore protective suits and double masks. The infants were isolated from their mothers immediately after delivery.”