Blood Test May Identify Higher Risk Pregnancies in Women Diagnosed with COVID-19

Anecdotal reports have reported potentially higher cases of stillbirths caused by certain SARS-CoV-2 variants, leading to increased concern in the scientific community. Scientists had identified a link between COVID placentitis, in which the virus infects the placenta, and these poor outcomes, but can only diagnose instances of placentitis after delivery by examining the placenta. A new study has now shown that a blood test may identify risk of stillbirth and placentitis in pregnant individuals who have had COVID-19.

The finding of the small preliminary study by researchers at Northwestern University (Evanston, IL, USA) builds on another study with similar results and could have implications in how physicians screen for and address high-risk pregnancies. The new study illuminates a link between placentitis and circulating SARS-CoV-2 virus. Placentitis affects between 1% and 2% of pregnant people infected with COVID-19. Unlike many pregnancy complications, the risk of placentitis and stillbirth is not linked to the severity of the virus. According to the researchers, predicting which placentas are at risk next to impossible, because an asymptomatic infection could just as easily have complications as a very sick person.

Using a biorepository of blood taken from pregnant people during the pandemic in 2020, the scientists looked at the blood of participants who had tested positive for COVID-19 during pregnancy - six who were positive for placentitis and 12 controls who were not. Then, the scientists looked for RNA of the virus in maternal blood using the same PCR-based test usually performed on nasal swabs. Out of those who had placentitis, two had low levels of viral RNA (called viremia) in their blood; none of the controls did. One of the people with viremia had a stillbirth, and the other had a well infant; all participants who tested negative for the marker delivered healthy babies.

Most pregnant patients with COVID-19 will go on to have normal pregnancies. Improved versions of this test and additional studies to validate the finding could help obstetricians develop plans for those who are at a high risk of placentitis and stillbirth, according to the researchers. They plan to conduct follow-up studies with larger pools of participants and hope other labs will build on the small body of literature to further validate the findings. The best way to protect both the parent and baby is to get vaccinated, the researchers said. In their observations, stillbirths have been more common in unvaccinated patients.

“Right now, we don’t know if there’s placentitis until after the fact,” said Northwestern’s Dr. Leena Mithal, the study’s first author. “We’re laying groundwork for further studies so that in the future, people who are diagnosed with COVID during pregnancy may be able to get a test that will help identify pregnancies that may be at higher risk of stillbirth or fetal distress.”

“The part of the placenta infected by the virus is also the part that’s in contact with maternal blood,” said Dr. Elisheva Shanes, a co-investigator of the study. “So if there’s infection in these cells, the virus may also be found in the blood. If a pregnant person had COVID and no placentitis, we wouldn’t expect to find virus in the blood.”

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