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NIH Record - 75th Anniversary - National Institutes of Health

Pregnant Women in Third Trimester Unlikely to Pass Covid-19 to Newborns

Pregnant woman torso with hand on baby bump

Pregnant women in their third trimester are unlikely to pass Covid-19 to their newborns.

Photo: Yacobchuk/iStock/Getty

Pregnant women who are infected with SARS-CoV-2, the virus that causes Covid-19, during the third trimester are unlikely to pass the infection to their newborns, suggests an NIH-funded study. The study—supported by NICHD, NHLBI and NIAID, and published in the JAMA Network Open—followed 127 pregnant women who were admitted to Boston hospitals during spring 2020. 

Among the 64 pregnant women who tested positive for SARS-CoV-2, no newborns tested positive for the virus. Data is still pending on women infected earlier in their pregnancies.

“This study provides some reassurance that SARS-CoV-2 infections during the third trimester are unlikely to pass through the placenta to the fetus, but more research needs to be done to confirm this finding,” said NICHD director Dr. Diana Bianchi.

The team found that pregnant women with Covid-19 had detectable levels of virus in respiratory fluids like saliva, nasal and throat secretions, but no virus in the bloodstream or the placenta. They also evaluated the development of maternal antibodies, and how well those antibodies passed through the placenta to the fetus (an indicator of potential immune protection from the mother). 

The researchers observed lower-than-expected levels of protective antibodies in umbilical cord blood. In contrast, they found high levels of influenza-specific antibodies, presumably from maternal flu vaccination, in the cord blood samples of both SARS-CoV-2 positive and negative women. The researchers suggest these findings may indicate that SARS-CoV-2 antibodies do not pass through the placenta as easily as other maternal antibodies.

These findings could help improve care of Covid-positive mothers and guide strategies for vaccinating them.

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