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,”and , of the division of pediatric infectious diseases at University of Alabama at Birmingham, wrote in their . “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, 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. 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.”
Two of the infants had elevated IgG and IgM concentrations. IgM “is not usually transferred from mother to fetus because of its larger macromolecular structure. ... Whether the placentas of women in this study were damaged and abnormal is unknown,” Dr. Zeng and colleagues said. “Alternatively, IgM could have been produced by the infant if the virus crossed the placenta.”
“Although these 2 studies deserve careful evaluation, more definitive evidence is needed” before physicians can “counsel pregnant women that their fetuses are at risk from congenital infection with SARS-CoV-2,” Dr. Kimberlin and Dr. Stagno concluded.
Dr. Dong and associates had no conflicts of interest. Their work was supported by the National Key Research and Development Project and others. Dr. Zeng and colleagues had no relevant financial disclosures. Their study was supported by grants from the National Natural Science Foundation of China and Zhongnan Hospital. Dr. Kimberlin and Dr. Stagno had no conflicts of interest.