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Infectious Diseases

12 June 2020

Clotting tied to Covid-19 may harm the placenta

Signs of reduced blood flow in the placentas of women infected with the new coronavirus have doctors concerned.

Women who had Covid-19 while pregnant showed evidence of placental injury, suggesting a new complication of the illness, researchers say.

The good news from the small study of 16 women is that "most of these babies were delivered full-term after otherwise normal pregnancies", said study senior author Dr Jeffrey Goldstein. He's assistant professor of pathology at Northwestern University Feinberg School of Medicine in Chicago.

However, signs of reduced blood flow in the placentas of women infected with the new coronavirus does have doctors concerned.

Right now, Covid-19 injury to the placenta "doesn't appear to be inducing negative outcomes in live-born infants, based on our limited data, but it does validate the idea that women with Covid should be monitored more closely," Goldstein said in a university news release.

Abnormal blood flow

The placenta provides the foetus with nutrients and oxygen from the mother, while at the same time removing waste.

In the research, the Chicago team examined the placentas of the women immediately after they gave birth. The researchers found signs of abnormal blood flow between the mothers and their babies.

All of the women had tested positive for Covid-19, but their symptoms varied. Five never developed any symptoms of coronavirus infection at all, the researchers noted. Four had flu-like symptoms three or four weeks prior to delivering their babies, while others showed symptoms at the time of delivery.

Only one baby was born prematurely; 14 others had normal delivery times and weights. One woman suffered a miscarriage in her second trimester.

Most "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," said study co-author Dr Emily Miller, assistant professor of obstetrics and gynaecology at Feinberg.

She explained that nature has equipped placentas to supply adequate nutrients to the foetus, even when placed under great strain.

Risk of compromised pregnancies

"Even with only half of it working, babies are often completely fine," Miller said in the release. "Still, while most babies will be fine, there's a risk that some pregnancies could be compromised."

According to the research team, two abnormalities were noted in the placentas studied: abnormal blood vessels involved in the transmission of blood from the mom to the foetus (a condition called maternal vascular malperfusion), and blood clots within the placenta, called intervillous thrombi.

Blood pressure was not an issue. Even though some women develop spikes in blood pressure during pregnancy (preeclampsia), the issue did not appear to affect the women in this study.

Still, "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."

The findings, published on 22 May in the American Journal of Clinical Pathology, suggest that doctors should closely monitor pregnant women during the coronavirus pandemic, according to the authors.

Closer monitoring might include non-stress tests, which assess how well the placenta is delivering oxygen, or growth ultrasounds, which measure if the baby is growing at a healthy rate, Miller said.

Disturbing findings

"Not to paint a scary picture, but these findings worry me," Miller said. "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. We must discuss whether we should change how we monitor pregnant women right now."

As to the one miscarriage noted in the report, "that patient was asymptomatic [for Covid-19], so we don't know whether the virus caused the miscarriage or it was unrelated," Goldstein said.

Two obstetricians who read over the new report agreed that the findings are cause for concern.

"This article has some very interesting yet disturbing findings," said Dr Mitchell Kramer, who directs obstetrics and gynaecology at Huntington Hospital in Huntington, New York. "There was damage noted in the placentas that is suggestive of changes caused by coronavirus infection, including inflammation and clot formation – basically, vascular damage."

Still, moms-to-be shouldn't be unduly alarmed, he said. "Much more study is needed and these findings may just be the tip of the iceberg, but so far the babies of pregnancies infected with Covid-19 do not appear to be adversely affected," Kramer said.

Dr Adi Davidov is associate chair of gynaecology at Staten Island University Hospital in New York City. He agreed that "as we learn more about Covid-19, we have realised that there is an increasing risk of clotting and it is not surprising that examination of the placenta reveals vascular malperfusion."

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