An overactive immune system during pregnancy could be harmful to the baby.

New research suggests fetal mice suffer brain damage when their mothers have an immune system boost due to illness or injury, a Johns Hopkins Medicine news release reported.

The team found the hippocampus (the region of the brain devoted to spatial navigation and memory) was smaller in mice exposed to an overactive immune system in the womb.

"Our research suggests that in mice, males may be more vulnerable to the effects of maternal inflammation than females, and the impact may be life long," says study leader Irina Burd, M.D., Ph.D., an assistant professor of gynecology/obstetrics and neurology at the Johns Hopkins University School of Medicine and director of the Integrated Research Center for Fetal Medicine. "Now we wonder if this could explain why more males have diseases such as autism and schizophrenia, which appear to have neurobiological causes."

The researchers mimicked maternal infection in pregnant mice which caused inflammation. This type of inflammation between 18 and 32 weeks of gestation has been linked to preterm birth and other issues such as an imbalance of immune cells in the brain.

The team gave saline injections to mice in  the womb while another group got injections of lipopolysaccharide (LPS) which causes inflammation.

The LPS group "showed poor motor skills and behavioral issues" than the saline group as well as hyperactivity. Sixty days later the mice's motor problems had been resolved but they were still hyperactive.

"All this time later, something was still going on in their brains," Burd said.

All of the symptoms such as the presence of fewer nerve cells still were present in adulthood.

Burd believes chronic inflammation plays a "key role" keeping the hippocampus from growing and inhibiting brain development.