Study Finds Placenta Might Account For Low Fetal COVID Transmission

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New research explains exactly why few pregnant women seem to pass COVID-19 to their newborns after birth, and it’s all about the placenta

As if expecting parents don’t have enough to worry about, the ongoing fear of passing along COVID-19 to their babies in utero has been an understandable concern of many over the course of the past two years. But new research published by the American Journal of Pathology seems to explain why fetal COVID transmission is low, even when a pregnant person experiences severe illness due to the virus.

Researchers from Boston University School of Medicine (BUSM) collected placenta from 16 pregnant people diagnosed with COVID-19 in their second or third trimesters, finding that they contained lower levels of an enzyme called angiotensin-converting enzyme 2 (ACE-2) than those without the virus. This enzyme allows the virus that causes COVID-19 to enter human cells and spread throughout the body, with the research seemingly indicating that the placenta “sheds off” ACE-2 as a way to “block [the virus] from being passed to the fetus,” noted one of study’s co-authors, Elizabeth S. Taglauer MD, Ph.D., an assistant professor of pediatrics at BUSM who has been studying the link between placenta and protection against COVID since 2020.

The study was conducted between July 2020 and April 2021, before COVID-19 vaccines became widely available to the general public, though multiple studies have shown that both the Pfizer-BioNTech and Moderna vaccines produce immune responses in pregnant and lactating people, also helping to bolster immunity in their infants after birth.

Using placenta tissue from two groups — one group with normal pregnancies and no confirmed COVID-19 diagnoses and the other with at least one positive COVID diagnosis during the second and/or third trimester — researchers used a microscope to evaluate the presence of ACE-2, which seems to account for why COVID transmission in utero remains low, even if the pregnant mother faces a serious battle with the disease.

These findings might help doctors and health experts better understand how COVID-19 enters cells, particularly since the placenta works like the lungs in utero, transporting oxygen and nutrition to the fetus while waste products, like carbon dioxide, are transported back to the mother, according to the Mayo Clinic. Controlling these enzymes might help prevent COVID infections — the ultimate end goal for all of us in this never-ending saga.

In a press release, Dr. Taglauer called the placenta “one of the few ‘success stories’ of the pandemic,” and we’re gonna go ahead and call it the unsung hero we never knew we needed.