COVID Doesn't Pass From Mom to Fetus During Pregnancy: Study

TUESDAY, Dec. 22, 2020 (HealthDay News) -- A new study may prove reassuring for expectant moms: Pregnant women who are infected with COVID-19 during their third trimester appear unlikely to pass the infection to their fetuses.

This study was conducted between April and June 2020 among women who came to one of three Boston area hospitals either for treatment of COVID-19 or for delivery.

None of the newborns of the 127 pregnant women, including 64 who had varying levels of illness from the virus, tested positive for the coronavirus.

"I think that's probably one of the more reassuring pieces to a patient, just that if you get COVID-19 in pregnancy, still there seems to be a relatively low chance that your fetus is going to be born with active COVID-19 infection," said study author Dr. Andrea Edlow, a maternal-fetal medicine specialist at Massachusetts General Hospital.

The study participants who had tested positive for COVID-19 included 36% who were asymptomatic, 34% who had mild disease, 11% who had moderate disease, 16% with severe disease and 3% with critical disease.

The study also included 63 pregnant women who tested negative for the virus and 11 reproductive-age women who were not pregnant, to provide comparison.

Researchers evaluated the levels of virus in respiratory, blood and placental tissue samples. They also looked for the development of maternal antibodies, how well those antibodies passed through the placenta to the fetus and examined placental tissue.

They found detectable levels of the virus in the women's saliva, nasal and throat secretions. They found no virus in the bloodstream or the placenta.

Though in this study none of the babies were born positive for COVID-19, the risk isn't zero, Edlow cautioned. Other studies have shown the range is quite low, however, much lower than in other viruses, including Zika or cytomegalovirus, she noted.

Another significant but less encouraging finding from the study is that the moms infected with COVID-19 did make antibodies to the virus but did not transfer them across the placenta as much as would be expected.

While finding lower-than-expected levels of protective antibodies in umbilical cord blood, researchers found high levels of influenza antibodies, possibly from maternal flu vaccination, according to the study.

In other viruses or vaccines, antibodies tend to be transferred at much higher levels, possibly for evolutionary reasons because babies can't develop their own antibodies until 6 months of age, Edlow said.

The study was published Dec. 22 in the journal JAMA Network Open.

The new findings may have implications over how the new COVID vaccine can affect pregnancy, according to an editorial accompanying the study.

"I don't think it's definitive, but it raises unanswered questions about whether maternal antibodies from COVID vaccination are going to help protect the baby the way we see with, for example, influenza vaccine," said editorial co-author Dr. Denise Jamieson, chair of the department of gynecology and obstetrics at Emory University School of Medicine in Atlanta.

The findings highlight the importance of ensuring that pregnant women are included in research, Jamieson said, because scientists need to better understand how medication and vaccines work specifically in pregnant women.

"I think it's a really exciting time. I think we now have the tools to end this pandemic. It's going take some time, and in the meantime, pregnant women need to be vigilant and continue to protect themselves, but I'm very optimistic knowing that pregnant women are going to have access to these [COVID] vaccines," Jamieson said.

Although children overall have more mild disease when contracting COVID-19, infants are at higher risk for severe disease. Pregnant women are also at increased risk of severe disease.

In past research, other viral infections and getting fevers in pregnancy were associated with increased risk for certain neurodevelopmental issues in offspring that include autism, ADHD, anxiety and depression, Edlow noted.

The researchers hope to follow up with the women from this study and their children in future research.

"There could be longer-term, more subtle neurodevelopmental effects or other effects on organ programming that could occur that are separate from birth defects or stillbirth or being born with COVID-19," Edlow said. "There are potentially more subtle effects that we'll probably need years to tease out."

More information

The World Health Organization offers additional information on COVID-19 and pregnancy.

SOURCES: Andrea Edlow, MD, MSc, assistant professor, obstetrics, gynecology and reproductive biology, and maternal-fetal medicine specialist, Division of Maternal-Fetal Medicine, Massachusetts General Hospital; Denise Jamieson, MD, MPH, chair, department of gynecology and obstetrics, Emory University School of Medicine, and chief, gynecology and obstetrics, Emory Healthcare, Atlanta; JAMA Network Open, Dec. 22, 2020