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Pregnant women who are infected with SARS-CoV-2, the virus that causes COVID-19, are unlikely to pass the infection to their newborns during the third trimester, a study funded by the National Institutes of Health suggests. The study followed 127 pregnant women who were admitted to Boston hospitals during the spring of 2020. Among the 64 pregnant women who tested positive for SARS-CoV-2, no newborn tested positive for the virus. NIH support was provided by Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), the National Heart, Lung, and Blood Institute (NHLBI), and the National Institute of Allergy and Infectious Diseases (NIAID).
“This study provides some reassurance that third-trimester SARS-CoV-2 infections are unlikely to pass through the placenta to the fetus, but more research is needed to confirm this finding,” said Diana W. Bianchi , MD, NICHD Director.
The study, published in the journal JAMA network open, was led by Andrea G. Edlow, MD, M.Sc., of Massachusetts General Hospital and Harvard Medical School.
Researchers studied the onset of SARS-CoV-2 infection in the third trimester of pregnancy, evaluating virus levels in samples of respiratory, blood and placental tissue, the development of maternal antibodies, how well those antibodies passed through from the placenta to the fetus (an indicator of possible immune protection of the mother) and examined the placental tissue. The reported results are limited to women in the third trimester because data on infected women during the first and second trimesters are still being collected and evaluated.
Among those who tested positive for SARS-CoV-2 in the study, 36% (23/64) were asymptomatic, 34% (22/64) had mild disease, 11% (7/64) had moderate disease, 16% ( 10/64) had severe illness and 3% (2/64) had critical illness. The study included, as comparators, 63 pregnant women who tested negative for SARS-CoV-2 and 11 women of reproductive age with COVID-19 who were not pregnant.
The team found that pregnant women who tested positive for SARS-COV-2 had detectable levels of virus in respiratory fluids such as saliva, nasal and throat secretions, but no viruses in the bloodstream or placenta.
The researchers found no significant differences between the levels of antibodies to SARS-CoV-2 produced by pregnant and non-pregnant women. However, the study team observed lower-than-expected levels of protective antibodies in the umbilical cord blood. In contrast, they found high levels of influenza-specific antibodies, presumably from maternal influenza vaccination, in umbilical cord blood samples from SARS-CoV-2-positive and negative women. The researchers suggest that these findings may indicate that SARS-CoV-2 antibodies do not cross the placenta as easily as other maternal antibodies.
The researchers believe that theirs is one of the first reports of transfer of SARS-CoV-2 antibodies to the fetus less than expected. Low transfer of these antibodies was seen regardless of the severity of the woman’s COVID-19 or whether she had an underlying health condition, such as obesity, high blood pressure, or diabetes. The study authors noted that it will be important to determine why these maternal antibodies are less likely to cross the placenta, and whether this reduced antibody transfer makes newborns more vulnerable to SARS-CoV-2 infection, compared to others. infections The authors added that it will be important to determine how lower levels of maternal antibodies to SARS-CoV-2 can affect the health outcomes of preterm babies because COVID-19 can increase the risk of preterm labor.
The study also found that the placentas of infected women were no different from those of uninfected women, although the risk of ischemia (reduced blood flow) in the placenta appeared higher for women with more severe COVID-19. Consistent with a previous report, the researchers also found that while the placenta expresses the main molecules used by SARS-CoV-2 to cause infection, the ACE2 receptor and the TMPRSS2 enzyme, the two molecules are rarely expressed together in the same location. , which may help explain why the virus rarely affects the placenta.
The researchers suggest that their findings could help improve the care of pregnant women with COVID-19 and their newborns, as well as provide information to aid in the development of new strategies to vaccinate pregnant women.
