Among the 64 pregnant women who tested positive for SARS-CoV-2, no newborns tested positive for the virus.
"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 Diana Bianchi, director of the Eunice Kennedy Shriver National Institute of Child Health and Human Development.
Currently, pregnant women are considered to be at an increased risk for severe illness from Covid-19 compared to those who are not pregnant, according to the Centers for Disease Control and Prevention (CDC). Pregnant women with Covid-19 may also be at an increased risk for adverse outcomes such as preterm birth.
The health agency notes that much is still unknown about the risks the virus poses to newborns born to mothers with Covid-19. There have been instances of newborns testing positive for the virus after birth, but it is unknown if the infection was picked up before, during or after birth from close contact with an infected person.
The results reported are limited to women in the third trimester because data on women infected during the first and second trimesters are still being collected and evaluated, according to the study, published in the journal JAMA Network Open.
The researchers suggest their findings could help improve the care of pregnant women with Covid-19 and of their newborns, as well as provide information to assist in the development of new strategies for vaccinating pregnant women.