Pregnant women infected with the coronavirus during the third trimester are unlikely to pass the infection to their newborns, government researchers found.
The study, published this week in JAMA Network Open, found that 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 Dr. Diana W. Bianchi, director of National Institute of Child Health and Human Development, which helped with the study.
Researchers included 127 pregnant women who were admitted to Boston hospitals during the spring in the study. The researchers looked at levels of the coronavirus in respiratory, blood and placental tissue samples and the formation of maternal antibodies and how well those antibodies traveled through the placenta to the fetus.
Of the 64 who tested positive, 23 of the women were asymptomatic, 22 had mild disease, seven had moderate disease, 10 had severe disease while two of them had critical disease. The study included 63 pregnant women who tested negative and 11 women with COVID-19 who were not pregnant for comparison.
Detectable virus loads were found in respiratory fluids such as saliva in the pregnant women who were positive for SARS-CoV-2, but no virus was found in the bloodstream or the placenta, according to the National Institutes of Health, which funded the study.
The researchers did not find significant differences in amounts of coronavirus antibodies made by pregnant and non-pregnant, but they did notice lower levels of protective antibodies in umbilical cord blood than expected. On the contrary, they found high levels of influenza antibodies, probably from maternal flu vaccinations, in the cord blood of both coronavirus positive and negative women.
The small transfer of these antibodies occurred regardless of the severity of COVID-19 or whether a woman had an underlying health condition such as diabetes or obesity. The study authors noted that it is important to learn why these antibodies are less likely to cross the placenta and if this could cause newborns to be more susceptible to SARS-CoV-2 infection than other infections.
The results of the study only include women in the third trimester since data collection and analysis on women infected during the first and second trimesters is ongoing.
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