How SARS-CoV-2 can cause stillbirth, study finds


During the pandemic, several studies have shown unvaccinated pregnant people are at a higher risk for delivering stillborn babies when infected with COVID-19.

Although other viral infections have also been linked to stillbirths, a new study suggests the coronavirus that causes COVID-19 may have a completely different way of impacting a developing fetus.

A 44-member international research team studied 64 stillbirth cases and four early neonatal deaths from 12 countries to determine how COVID-19 caused perinatal deaths. All the expecting mothers were unvaccinated.

Based on their findings, they concluded the COVID-19 infection destroyed the placenta, depriving the fetus of oxygen, according to the report published Thursday in Archives of Pathology & Laboratory Medicine. Researchers determined the virus reaches the placenta and causes it to fail by passing through the mother’s bloodstream, a process known as viremia.

“Our study identified placental insufficiency as the root cause for stillbirths in women with COVID-19 during pregnancy,” said Dr. David Schwartz, an Atlanta-based pathologist who led the study. “Among the 68 cases, an average of 77% of the placenta had been destroyed and rendered useless for supporting critical fetal needs, resulting in stillbirth or early neonatal death.”

In all the studied cases, researchers found the placentas from infected mothers had a severe abnormality called SARS-CoV-2 placentitis, Schwartz said. Researchers found viral-induced lesions in the placenta blocked maternal and fetal blood flow and oxygen, killing placental tissues and causing “irreparable damage.”

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In almost all the cases, researchers also found increased fibrin – a key protein involved with blood clotting – was so “massive” it blocked blood and oxygen flow to the placenta. All the placentas also showed dead cells made up the major cell barrier between the mother and fetus, known as trophoblast necrosis.

Another placental complication that may have been caused by the virus was a rare accumulation of inflammatory cells called chronic histiocytic intervillositis, which was seen in 97% of cases studied by the international research team.

While the study may provide some insight into mechanisms of COVID-19 in a pregnant person, it’s probably not the whole story, said Dr. Catherine Spong, professor and chair of the department of obstetrics and gynecology at the University of Texas Southwestern Medical Center.

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The study did not include when mothers contracted COVID-19, the state or size of the placenta before infection, or enough pre-existing conditions that could affect the vital organ. The study also did not compare stillbirth placentas with those of people who had live births and were also infected.

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“It’s a piece of the puzzle,” she said of the study’s findings, “but it is just the beginning to really understand (COVID’s) impact in pregnancy.”

Researchers assumed many of the infections were from the delta variant, not omicron. While plenty of viral destruction was found in the placenta, post-mortem examinations showed a small number of fetuses had the virus in their internal organs. Despite this finding, researchers determined “there were no autopsy outcomes relating to the (virus) that would have accounted for their deaths.”

Other viral, bacterial and parasitic infections that occur in pregnancy and cause stillbirth travel through the placenta and damage the fetal organs, Schwartz said, but SARS-CoV-2 appears to stop at the placenta and do the most damage there.

“The placental destruction is so severe that whether or not the fetus becomes infected might be irrelevant,” he said.

While COVID-19 infection is associated with an increased risk of stillbirths, it’s uncommon. A November study released by the Centers for Disease Control and Prevention found stillbirths were documented in about 1.26% of deliveries with COVID-19 from March 2020 to Sept. 2021.

However, health experts say being unvaccinated is not worth the risk. As of Feb. 5, about 67% of pregnant people ages 18 to 40 were fully vaccinated against COVID-19. About 7% of them received the vaccine during pregnancy, according to CDC data.

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Studies have shown the COVID-19 vaccine is safe and effective for both the expectant parent and baby. Health experts say antibodies from the vaccine can pass through to the fetus and protect the baby from COVID-19 after birth.

An observational study of more than 24,000 newborns in Israel found “no evident differences” between newborns of women who received the Pfizer-BioNTech vaccine during pregnancy and those of women who were not vaccinated. Study authors said the findings contributed to current evidence establishing the safety of prenatal vaccine exposure, according to the report published Thursday in JAMA Pediatrics.

“Women should get vaccinated in pregnancy, as well as (before) pregnancy,” Spong said. “COVID can cause severe disease so vaccination is very important.”

Follow Adrianna Rodriguez on Twitter: @AdriannaUSAT. 

Health and patient safety coverage at USA TODAY is made possible in part by a grant from the Masimo Foundation for Ethics, Innovation and Competition in Healthcare. The Masimo Foundation does not provide editorial input.

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