Covid-19 infection in pregnancy, even with no symptoms, could harm a developing baby, research at UK College of Medicine finds

By Elizabeth Chapin
University of Kentucky

Covid-19 infection during pregnancy, even with no symptoms, could still have potential long-term consequences for a developing baby, according to a new University of Kentucky College of Medicine study.

UK staff scientist Brianna Doratt and Ihlem Messoudi,
Ph.D., right, in their lab (UK photo by Mark Cornelison)

The study led by Ilhem Messoudi, chair of the Department of Microbiology, Immunology and Molecular Genetics, was published in Cell Reports May 25. It shows that Covid infection in pregnant mothers who had no symptoms or mild symptoms still triggered immune responses that caused inflammation in the placenta.

“Prior to this study, this response was only thought to occur in severe Covid-19 cases,” said Messaoudi. “We now know that even a mild infection that doesn’t even register with a patient is still being registered by the maternal immune system. The placenta had very clear signs of having sensed that there was an infection.”

Because the placenta protects a developing fetus from many pathogens, transmission of viruses between mother and baby is extremely rare. The greatest risk for a fetus is how the mother’s immune system responds to the virus.

Immune responses triggering inflammation of the placenta can be linked to adverse pregnancy outcomes including pre-term labor and pre-eclampsia, as well as neonatal complications due to reduced immune function of the baby, Messaoudi says.

Messaoudi’s team analyzed immune cells in placenta tissue and blood from pregnant mothers who tested positive for the coronavirus. Samples from women with no symptoms or mild symptoms were compared to those without infection.

They found that patients testing positive had activated T-cells, an immune response, they had reduced levels of specialized macrophage cells that regulate the tissue. The immune cells in the placenta were “rewired” in a way that made the tissue more prone to inflammation.

The findings add to scientists’ growing understanding of the maternal immune system's relationship with the virus and will help lead to future studies on potential long-term impacts for mothers and babies.

“This tells us how capable the maternal immune system is … while at the same time shows how detrimental Covid-19 can be even when the infection is not severe,” Messaoudi said. “These are all reasons why it’s so important that pregnant mothers get vaccinated.”