This article is part of Harvard Medical School’s continuing coverage of COVID-19.
A growing body of evidence has linked the delta variant of SARS-CoV-2, the virus that causes COVID-19, with an increased risk for pregnancy complications, including stillbirths. Now, for the first time, Harvard Medical School researchers at Massachusetts General and Brigham and Women’s hospitals have detected the delta variant in the blood and placentas of women who had stillbirths and serious pregnancy complications. Their findings are reported in the Journal of Infectious Diseases.
Earlier studies indicated that COVID-19 poses a threat to pregnant women and fetuses. Recently, suspicion that the delta variant may be particularly dangerous during pregnancy has increased.
In late November 2021, the U.S. Centers for Disease Control and Prevention reported that pregnant women with COVID-19 were four times more likely to have miscarriages than uninfected pregnant women during the period when the delta variant was causing the majority of SARS-CoV-2 infections in the United States.
Earlier in the pandemic, before delta became the dominant strain in the United States, Andrea Edlow, HMS assistant professor of obstetrics, gynecology and reproductive biology and a maternal-fetal medicine specialist at Mass General, and several colleagues had studied 64 pregnant women with COVID-19 and found that none had detectable levels of SARS-CoV-2 in their blood or placentas.
But as the delta variant swept across the country in 2021, Edlow began to have her own suspicions.
“It seemed like we were seeing even more sick moms and a disproportionate number of stillbirths,” said Edlow. Stillbirth describes the death of a fetus after 20 weeks of pregnancy.
Edlow and her team received permission to analyze nasal swabs, umbilical cord blood, and placentas of three women who tested positive for COVID-19 late in their pregnancies. None had been vaccinated against the coronavirus.
Two of the women had stillbirths and a third woman’s fetus experienced distress and was delivered by urgent cesarean section. These blood and tissue samples underwent viral sequencing at Brigham and Women’s in the translational virology laboratory directed by Jonathan Li, an HMS associate professor of medicine.
The results were striking.
“All the moms had detectable virus in the bloodstream. All had high levels of detectable virus in their nasal swabs. All had infected placentas,” said Edlow. Viral sequencing confirmed that each woman was infected with the delta variant of SARS-CoV-2.
“This was definitely different from what we saw with the ancestral strain of SARS-CoV-2 during the first part of the pandemic,” Edlow said
Li noted that while COVID-19 is widely thought of as a pulmonary disease, studies indicate that when SARS-CoV-2 enters the bloodstream it can travel throughout the body and cause organ failure and other severe complications.
“Our testing showed that the virus was widely disseminated in these three patients,” said Li.
This appears to have resulted in severe inflammation of the placenta, which likely caused the stillbirths and complications. “This represents another example of the systemic manifestations of COVID-19,” he said.
Why the delta variant is a greater threat to pregnancy than earlier strains of SARS-CoV-2 is unknown, as is the potential impact of omicron, the variant identified by the WHO in November 2021.
However, Edlow said she hopes these findings can help bolster public health messaging aimed at battling misinformation that may lead some pregnant women to fear COVID-19 vaccines.
She noted that more than 170,000 pregnant women have been vaccinated and, reassuringly, there’s no evidence that the injections increased the risk for birth defects or any form of pregnancy complications.
“Yet stillbirth, preterm birth, and poor neonatal outcomes are all associated with getting COVID-19,” said Edlow. “If you want to do the best thing for your baby, get vaccinated.”
Funding for this work came from the Eunice Kennedy Shriver National Institute of Child Health and Human Development and the March of Dimes.