News release
Tuesday December 22, 2020
Pregnant women infected with SARS-CoV-2, the virus that causes COVID-19, are unlikely to transmit 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 in the spring of 2020. Of the 64 pregnant women who tested positive for SARS-CoV-2, no newborns tested positive for the virus. NIH support was provided by the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), National Heart, Lung and Blood Institute (NHLBI), and National Institute of Allergy and Infectious Diseases (NIAID).
“This study provides some assurance that SARS-CoV-2 infections are unlikely to pass through the placenta to the fetus during the third trimester, but more research needs to be done to confirm this finding,” said Diana W. Bianchi, MD, NICHD Director.
The study, published in the journal JAMA Network Open, was directed by Andrea G. Edlow, MD, M.Sc., of Massachusetts General Hospital and Harvard Medical School.
The researchers studied the occurrence of SARS-CoV-2 infection in the third trimester of pregnancy, evaluated the virus levels in respiratory, blood and placental tissue samples, the development of maternal antibodies, how well those antibodies passed through the placenta to the fetus (an indicator of possible immune protection of the mother) and examined placental tissue. The reported results are limited to women in the third trimester, as data on women infected during the first and second trimester is still being collected and evaluated.
Of 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 were positive for SARS-COV-2 had detectable levels of virus in respiratory fluids such as saliva, nose and throat secretions, but no virus in the bloodstream or placenta.
The researchers found no significant differences between levels of SARS-CoV-2 antibodies produced by pregnant and non-pregnant women. However, the research team observed lower than expected levels of protective antibodies in cord blood. In contrast, they found high levels of influenza-specific antibodies, presumably from maternal flu vaccination, in the umbilical cord blood samples of both 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 readily as other maternal antibodies.
The researchers believe theirs is one of the first reports of a less than expected transfer of SARS-CoV-2 antibodies to the fetus. Low transmission of these antibodies was observed regardless of the severity of COVID-19 in the woman and 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 transmission makes newborns more vulnerable to SARS-CoV-2 infection, compared to other infections. The authors added that it will be important to determine how lower levels of maternal SARS-CoV-2 antibodies may affect preterm infants’ health outcomes, as COVID-19 may increase the risk of preterm birth.
The study also found that placentas from infected women were no different from those from uninfected women, although the risk of ischemia (decreased blood flow) in the placenta seemed higher for women with more severe COVID-19. Consistent with a previous report, the researchers also found that although the placenta expresses important molecules used by SARS-CoV-2 to cause infection – the ACE2 receptor and the TMPRSS2 enzyme – the two molecules rarely co-exist. expressed in the same location, which may help explain why the virus rarely attacks the placenta.
The researchers suggest their findings could help improve care for pregnant women with COVID-19 and their newborns, as well as provide information to aid in the development of new strategies for vaccinating pregnant women.
About the Eunice Kennedy Shriver National Institute for Child Health and Human Development (NICHD): NICHD leads research and training to understand human development, improve reproductive health, improve the lives of children and adolescents, and optimize skills for all. For more information, visit https://www.nichd.nih.gov.
About the National Institutes of Health (NIH):
NIH, the national medical research agency, includes 27 institutes and centers and is part of the United States Department of Health and Human Services. NIH is the premier federal agency that conducts and supports basic, clinical and translational medical research, investigating the causes, treatments, and cures for both common and rare diseases. For more information about NIH and its programs, visit www.nih.gov.
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Article
Edlow AG, et al. Assessment of maternal and neonatal SARS-CoV-2 viral load, transplacental antibody transfer and placental pathology in pregnancies during the COVID-19 pandemic. JAMA Network Open DOI: 10.1001 / jamanetworkopen.2020.30455 (2020)