Some babies who experience a COVID-19 infection in utero face nearly double the risk of neurodevelopmental disorders, researchers say.

In a new study looking at electronic health records for 18,355 births since the start of the pandemic, researchers found a significant uptick in developmental issues among boys in their first year of life if their mothers tested positive for SARS-CoV-2 — the virus that causes COVID-19 — during pregnancy. No similar increase was seen in girls.

“The neurodevelopmental risk associated with maternal SARS-CoV-2 infection was disproportionately high in male infants, consistent with the known increased vulnerability of males in the face of prenatal adverse exposures,” said Dr. Andrea Edlow, an associate professor of obstetrics, gynecology and reproductive biology at Massachusetts General Hospital and a co–lead author of the study published this month in the journal JAMA Network Open.

Of the children studied, 883 were exposed to COVID-19 in utero and 3% of this group of kids received a diagnosis of a neurodevelopmental disorder before their first birthday. By contrast, just 1.8% of the babies who were not exposed during pregnancy received a similar diagnosis.

When the researchers accounted for race, ethnicity, insurance status, hospital type, maternal age and preterm status, they found that COVID-19 exposure during pregnancy was associated with an almost two-times higher rate of neurodevelopmental diagnosis among boys by 12 months, but no difference for girls. The risk was slightly lower at 18 months, the study found.

Not enough of the mothers in the study were vaccinated against COVID-19 to assess whether that made any difference, the researchers said.

Previous studies have pointed to a link between other sorts of infections in pregnancy and an elevated risk for autism and other neurodevelopmental disorders. While the latest findings suggest that this risk extends to COVID-19 as well, the researchers said that more work is needed to know for sure.

“We hope to continue to expand this cohort, and to follow them over time, to provide better answers about any longer-term effects,” said Dr. Roy Perlis, associate chief of research in the Department of Psychiatry at Massachusetts General Hospital and co–lead author of the study.