Preliminary study finds injury to placenta in pregnant women with COVID-19

A small study of women who tested positive for COVID-19 while pregnant found evidence of injury to the placenta, an organ that develops in the mother’s uterus and provides oxygen and nutrients to the growing baby.

Researchers conducted pathological exams of placentas immediately after birth and found insufficient blood flow from the mother to the fetus, as well as blood clots in the placenta. 

The study, published May 22 in the journal American Journal of Clinical Pathology, involved only 16 women. But it is the largest study to examine the health of placentas in women who tested positive for COVID-19 to date.

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Researchers say the findings, though early, could help inform how pregnant women should be clinically monitored during the pandemic.

“Not to paint a scary picture, but these findings worry me,” said study co-author Dr. Emily Miller, a Northwestern Medicine obstetrician. “I don’t want to draw sweeping conclusions from a small study, but this preliminary glimpse into how COVID-19 might cause changes in the placenta carries some pretty significant implications for the health of a pregnancy.”

The placenta is the first organ to form in fetal development, acting as the fetus’ lungs, gut, kidneys and liver. It takes oxygen and nutrients from the mother’s blood stream and eliminates all metabolic waste. It’s also responsible for many of the hormonal changes within the mother’s body.


A file image shows a doctor performing an ultrasound examination on a pregnant woman. (Photo credit: JASPER JACOBS/AFP via Getty Images)

“They were healthy, full-term, beautifully normal babies, but our findings indicate a lot of the blood flow was blocked off and many of the placentas were smaller than they should have been,” Miller said. “Placentas get built with an enormous amount of redundancy. Even with only half of it working, babies are often completely fine.”

All of the babies who were born tested negative for COVID-19, the study said. Fourteen of the babies were born full term and with normal weights and Apgar scores. One live-born infant was premature. 

The 16 women in the study delivered their babies at Northwestern Medicine Prentice Women’s Hospital between March 18 and May 5, and all tested positive for COVID-19. 

Researchers said 15 patients delivered live babies in the third trimester. One patient had a miscarriage in the second trimester, but she “was asymptomatic, so we don't know whether the virus caused the miscarriage or it was unrelated," said senior author Dr. Jeffrey Goldstein, a Northwestern Medicine pathologist. 

The study found that 12 of the women had a type of injury that can impair blood flow from the mother to the fetus called, vascular malperfusion. Six of them had blood clots to the placenta.

“There is an emerging consensus that there are problems with coagulation and blood vessel injury in COVID-19 patients,” Goldstein said. “Our findings support that there might be something clot-forming about coronavirus, and it’s happening in the placenta.”

But Goldstein said that the virus doesn’t appear to be “inducing negative outcomes in live-born infants, based on our limited data.” 

Researchers acknowledged the small size of the study, but said the findings suggest that pregnant women should be monitored more closely. Miller said this could include non-stress tests, which examine how well the placenta is delivering oxygen, or growth ultrasounds, which measure if the baby is growing at a healthy rate.

“We must discuss whether we should change how we monitor pregnant women right now,” Miller said.

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This story was reported from Cincinnati.