According to a study led by UCL researchers with Great Ormond Street Hospital for Children and the NIHR Great Ormond Street Biomedical Research Centre, it is only possible for an unborn baby to contract Covid-19 if their gut is exposed to the SARS-CoV-2 virus.
The research was published in the ‘BJOG – An International Journal of Obstetrics & Gynaecology Journal’. Although the study did not look specifically at mothers with Covid-19 and whether their infection was transmitted to an unborn baby, it found that certain fetal organs, such as the intestine, are more susceptible to infection than others.
However, researchers said, that opportunities for the Covid-19 virus infecting the fetus are extremely limited, as the placenta acted as a highly effective and protective shield, and evidence suggested fetal infection, known as vertical transmission, is extremely uncommon.
Researchers set out to understand how newborn babies could have developed Covid-19 antibodies, as it had been reported in a small number of cases.
Specifically, they wanted to know if and how the virus could be passed from an infected mother to the unborn fetus.
To answer this question, researchers examined various fetal organs and placenta tissue to see if there was any presence of the cell surface protein receptors, ACE2 and TMPRSS2. These two receptors sit on the outside of cells and both are needed for the SARS-Cov-2 virus to infect and spread.
Researchers found the only fetal organs to feature both the ACE2 and TMPRSS2 were the intestines (gut) and the kidney; however, the fetal kidney is anatomically protected from exposure to the virus and is, therefore, less at risk of infection.
Therefore, the team concluded that the SARS-CoV-2 virus could only infect the fetus via the gut and through fetal swallowing of amniotic fluid, which the unborn baby does naturally for nutrients.
After birth ACE2 and TMPRSS2 receptors are known to be present in combination on the surface of cells in the human intestine as well as the lung. The gut and lung are suspected to be the main routes for Covid-19 infection, but in younger children, the intestine appeared to be most important for virus infection.
Senior author, Dr Mattia Gerli (UCL Division of Surgery and Interventional Science & the Royal Free Hospital) explained, “The fetus is known to begin swallowing the amniotic fluid in the second half of pregnancy. To cause infection, the SARS-CoV-2 virus would need to be present in significant quantities in the amniotic fluid around the fetus.”
“However, many studies in maternity care have found that the amniotic fluid around the fetus does not usually contain the SARS-CoV2 virus, even if the mother is infected with Covid-19. Our findings, therefore, explain that clinical infection of the fetus during pregnancy is possible but uncommon and that is reassuring for parents-to-be,” Gerli added.