New evidence suggests coronavirus transmission from mother-to-baby may be possible in the womb.
The study, published in the Journal of the American Medical Association (JAMA), identified a type of antibody, or immune protein, known as IgM in the blood of two infants born to mothers with the novel coronavirus (SARS-CoV-2). Although not proven, this could be the first evidence of so-called 'vertical transmission' of the novel coronavirus in the womb, rather than during or shortly after birth.
The accompanying editorial wrote that the finding 'deserves careful consideration', but added that 'at this time, these data are not conclusive and do not prove in utero transmission.'
The research team, led by Dr Hui Zeng at Wuhan University in China, reviewed clinical records of six mothers with coronavirus and their babies at the Zhongnan Hospital of Wuhan. Although the mothers were separated from their babies to prevent virus transmission, two babies had high levels of IgM antibodies against the virus in their blood at birth.
The IgM antibodies found are usually too large to cross the placenta, leading the authors to speculate that the babies had mounted an immune response themselves against the virus. However, there was no other evidence of the virus at birth using a diagnostic test. Experts have therefore cautioned that the presence of IgM antibodies doesn't necessarily indicate infection with coronavirus in the womb.
'Whilst this could indicate an infection in utero, the fact that the two infants had no detectable virus at the time of birth renders transplacental infection in utero unlikely,' said Professor Richard Tedder, visiting professor of medical virology at Imperial College London, who was not involved in the study.
Another theory suggested by the authors, is that maternal IgM antibodies were transferred across a damaged placenta, although this was not determined. If the antibodies did originate from the mother, they may provide some degree of immunity in the baby to the virus.
However, this would be short-lived, noted Dr Simon Clarke, associate professor of cellular microbiology at the University of Reading, not involved in the study. He said: 'Even if the antibodies were protective, and there is no evidence of that, any immunity would dwindle because B-cells which produce the antibodies, are not transferred.'
A second study, published in JAMA the same day, identified a third infant with IgM antibodies against the novel coronavirus.
Previous reports have described novel coronavirus infection in newborn babies to virus-positive mothers, but have not been able to rule out that transmission occurred outside of the womb. One such study, also published in JAMA, examined 33 babies born to mothers with COVID-19. Strict infection controls were followed during delivery. The authors, from two children's hospitals in Wuhan and one in Shanghai, discovered that three babies were born with COVID-19 and that all babies recovered from the disease.
Dr David Kimberlin, a professor of paediatric infectious diseases at the University of Alabama, Birmingham, who was not involved in the study said 'For now, this study serves as a sort of proof of principle that COVID-19 transmission is possible, but not whether it's likely.'