Pregnant women who contract coronavirus in 3rd trimester unlikely to pass infection to newborn, study finds

In a study of pregnant women who were admitted to Boston hospitals during the spring of 2020, those who contracted coronavirus during the third trimester were unlikely to pass the infection on to their newborns. The study, funded by the National Institutes of Health (NIH), was published in the journal JAMA Network Open.

It included data from 127 pregnant women, 64 of whom tested positive for SARS-CoV-2. Of this group, 3% had critical disease, 16% developed severe disease, 11% had moderate disease, 34% had mild disease and 36% were asymptomatic. None of the newborns born to those 64 women tested positive for the virus.

The pregnant women who tested positive had detectable levels of the virus in respiratory fluids like saliva, nasal and throat secretions, but no virus in the bloodstream or placenta, researchers said. They also noted lower-than-expected levels of protective antibodies in umbilical cord blood, suggesting that the antibodies do not pass through the placenta as easily as other antibodies such as those from the flu vaccine.

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“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,” Diana W. Bianchi, M.D., Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) director, said.

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.

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Most newborns who have tested positive usually have mild or no symptoms and recover, according to the CDC, although there have been instances of newborns with severe COVID-19.