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Four things to know about the new Boston-based research on COVID-19 and pregnant women

In this May 7, 2020 file photo, a pregnant woman wearing a face mask and gloves holds her belly as she waits in line for groceries at St. Mary's Church in Waltham.Charles Krupa/Associated Press

Two new studies conducted at Massachusetts General Hospital and Brigham and Women’s Hospital looked at pregnant women who had COVID-19 or who received COVID-19 vaccinations. Some of the findings were surprising, STAT News reports. Here are some key takeaways:

Mothers expecting male babies make less antibodies against COVID-19

Mothers with COVID-19 who have male fetuses make lower levels of antibodies against the virus than mothers with female fetuses, MGH said in a statement. Mothers with male fetuses also transfer fewer antibodies to the fetus.

The finding suggested males may be more vulnerable to getting infected with the coronavirus in infancy and demonstrates that the sex of the fetus can influence the maternal immune response to the virus, Dr. Andrea Edlow, a maternal-fetal medicine specialist at MGH who co-led the new studies, said in the statement.


“What’s striking here is that the mothers who are carrying male babies have much lower levels of antibodies to the coronavirus,” Akiko Iwasaki, a virologist and immunologist at Yale University who was not involved in the study, told STAT. “What’s interesting about that is it means that the sex of the baby can dictate how the mother responds to a viral infection.”

Pregnant and lactating women didn’t react as much to the first vaccine shot

STAT also reports that pregnant and lactating women didn’t make as many antibodies following the first shot of either the Pfizer or Moderna vaccine, though after the second shot, those differences more or less disappeared.

“Pregnant and lactating individuals had what we called delayed kinetics, sort of a delayed arrival to the same point as non-pregnant individuals,” Edlow told STAT.

“What we really showed with these data is that especially for pregnant and lactating individuals, it’s very, very important to adhere to that strict schedule for the Pfizer and Moderna vaccines.”


Male fetuses did wage a defense against the virus, but there’s concern it could go too far

Researchers looked at samples from placentas, which grow from the developing embryo’s cells and provide the embryo with oxygen and nutrients. They found that male placentas demonstrated significantly higher levels of certain genes and proteins associated with increased immune activation compared with female placentas, MGH said.

That increased immune activation could help protect male fetuses from becoming infected with the coronavirus, but the resulting inflammation could also pose risks to the fetus and child.

Edlow said in a telephone interview it was a “delicate balance” and further research was needed to determine if the increased immune activation was beneficial.

“What the downstream effects are going to be for the child we still don’t know,” Edlow told STAT. “But it’s definitely going to be important to follow up the development of these children on the basis of sex because we see these really profound changes in the placenta that suggest that the intrauterine environment is suddenly altered even in the setting of mild maternal disease.”

Officials and experts say pregnant women should get vaccinated

Ruth Karron, a virologist and pediatric infectious diseases professor at the Johns Hopkins Bloomberg School of Public Health, told STAT that, while the results are intriguing and worthy of follow-up, she didn’t see them immediately changing the clinical care of pregnant people.

“These are exploratory analyses of functional antibodies that may or may not correlate with protection,” Karron said. “The data is of interest, but I think it doesn’t at this time have practical implications in terms of vaccine rollout other than what we already know — which is that 97% of pregnant people who have been hospitalized with COVID in this country are unvaccinated. So even as we learn more about the science and explore these differences, it’s very important that we keep focused on the fact that vaccination is protective.”


Health officials have urged women who are pregnant, planning to become pregnant or currently breastfeeding, to get vaccinated against the coronavirus as soon as possible. The US Centers for Disease Control and Prevention says the data suggest that the benefits outweigh the risks. People who are pregnant or recently pregnant are more likely to get severely ill than others, are at increased risk of preterm birth, and might be at increased risk of other adverse pregnancy outcomes.

Vaccination while pregnant may also help protect babies against COVID-19, according to the CDC.

Martin Finucane can be reached at