There is a very low risk that pregnant women with COVID-19 will pass the virus to their unborn babies, researchers say.
The study should reassure expectant parents, said the British investigators.
To find out if and how the virus could pass from an infected pregnant women to her fetus, the team examined various fetal organs and placenta tissue for two cell surface protein receptors (ACE2 and TMPRSS2) needed by the virus to infect cells and spread.
The only fetal organs with both of the receptors are the intestines and the kidney, but a fetus' kidney is anatomically protected from exposure to the virus and therefore at little risk of infection.
That means that the virus can only infect the fetus via the intestine through swallowing of amniotic fluid, which the unborn baby does naturally for nutrients, according to the researchers.
"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," said study co-author Mattia Gerli of University College London and Royal Free Hospital.
"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 said in a news release.
The findings were recently published in BJOG – An International Journal of Obstetrics & Gynaecology.
"We have shown that the fetal intestine, which is in contact with amniotic fluids swallowed by the baby, is susceptible to SARS-CoV-2 virus. However, the placenta acts as a natural barrier, and with the limited evidence of amniotic fluid containing the virus, our study should provide reassurance to mothers," added study co-author Dr. Paolo De Coppi, a professor at UCL Great Ormond Street Institute of Child Health.
The greatest risk to the fetus during pregnancy is if the mother becomes seriously ill with COVID, the authors note. The virus might then be present in high concentration in the amniotic fluid. This could also trigger preterm birth.
Vaccination against COVID-19 is the best way to protect the baby and mother, the researchers said.
The U.S. Centers for Disease Control and Prevention has more on pregnancy and COVID-19.
SOURCE: University College London, Nov. 19, 2021