While the risk of developmental delays was low overall, it rose to about 6% among babies who were exposed to COVID in the womb, while unexposed infants’ risk was about 3%, according to findings released Thursday in the journal JAMA Network Open. The lags were seen in behaviors such as rolling over, reaching for objects or babbling—basic milestones of infancy. 

COVID has already been shown to affect a wide variety of the body’s systems and organs, including the lungs, heart and nerves. The study of electronic health records from more than 7,000 obstetric patients at Massachusetts hospitals, including those of 222 pregnant patients with COVID, along with their children’s, is another indication of the pandemic’s potential long-lasting impact.

“It’s going to be important to watch this cohort grow, to see how these children will look in 18 months and two years,” said senior author Roy Perlis, director of the Center for Quantitative Health at Massachusetts General Hospital in Boston. 

For now, he said, “If our study encourages more pregnant moms to get vaccinated, or more people considering becoming pregnant to go get vaccinated, that would be fantastic.”

The study accounted for race, age and other factors that could explain the different rates of developmental delays. Much more research is needed to determine how much risk COVID poses to fetal brain development and how best to minimize it, according to an accompanying commentary in the journal.

The study could not assess the impact of vaccination because it examined records from pregnancies between March and September of 2020, before COVID shots were available. Most of the patients with COVID had mild cases, Perlis said, so the impact of disease severity could not be measured either. 

The study did find that catching Covid during the third trimester—which is especially critical for brain development—appeared to add more risk than earlier in pregnancy. 

The findings fit with previous studies linking various infections during pregnancy with increased risk of autism, schizophrenia and other brain conditions in offspring, as well as recent research showing that COVID affects brain cells.