COVID Infection Can Attack Placenta, Triggering Stillbirth

Unlike other fungal, bacterial or viral infections, which cross over the placenta to affect the fetus, SARS-CoV-2 is particularly lethal to the developing placenta, and this damage deprives the fetus of oxygen and nutrition, said study author Dr. David Schwartz, a perinatal pathologist in Atlanta.

In November, the U.S. Centers for Disease Control and Prevention reported that pregnant women with COVID are at increased risk for stillbirths, which is the loss of a baby before or during delivery. The risk remains rare, Schwartz said.

To better understand why risk of stillbirth may be increased in expectant women with COVID, Schwartz and his team analyzed placentas from 64 stillbirths and four cases in which babies soon died after birth. All of the pregnant women were unvaccinated.

Infected placentas showed increased levels of fibrin, a protein involved with blood clotting, and obstructed blood and oxygen flow to the placenta. All 68 of the placentas also had death of cells that comprise the major protective barrier between mother and fetus, and 66 had a buildup of inflammatory cells called chronic histiocytic intervillositis, the study showed.

"We saw these abnormalities under the microscope and with the naked eye," Schwartz said. "The average placenta was 77.7% destroyed. A fetus can't survive with this type of damage because the placenta is its sole source of oxygen and nutrition."

While a small number of fetuses did show signs of infection, there was no evidence that the stillbirths were caused by COVID, he said.

Other illnesses infect the placenta typically by crossing over into the fetus, where they can cause damage to its organs, Schwartz explained. By contrast, the damage with COVID-19 takes place solely in the placenta, the study found. This is so unique that it now has its own name: SARS-CoV-2 placentitis, he said.

There’s reason to believe that getting vaccinated against COVID-19 may reduce these risks. The SARS-CoV-2 virus reaches the placenta by traveling through the mother's bloodstream.

"If we can block the presence of the virus in the mother's bloodstream during pregnancy, we assume there would be no placental infection," Schwartz said.

Unvaccinated pregnant women are known to be at greater risk for more severe COVID-19.

"Pregnant women be should be vaccinated for their own safety, but these vaccines are also potentially lifesaving for the fetus," Schwartz said.

The findings were published online Feb. 10 in the Archives of Pathology & Laboratory Medicine.

Dr. Christina Han, division director of maternal and fetal medicine at the University of California, Los Angeles, reviewed the findings.

"The authors should be applauded for this important study that correlates severe placental abnormalities to severe fetal-neonatal adverse outcomes,” she said.

But, Han added, the study does not prove cause and effect.

"We cannot say definitively that COVID-19 caused these findings," she said, adding that more research is needed before drawing any conclusions.

"It is important for pregnant individuals to note that the risk of stillbirth likely remains low, but the placenta and fetus are not immune to COVID-19 infection," Han said.

"The most important takeaway is that prevention of COVID infection via primary prevention -- i.e. masking and vaccination [including boosters] -- is critical to protect our pregnant individuals and their fetuses," she said.

The vaccine is safe for mom and baby, Han said.

The Society for Maternal-Fetal Medicine, the CDC and other medical groups recommend COVID-19 vaccination for women who are pregnant, recently pregnant, trying to become pregnant now, or who might become pregnant in the future.