(Reuters Health)

Pregnancy may trigger changes in the structure and size of regions in a woman’s brain that are involved in responding to social and emotional cues, a recent study suggests.

Many of these changes appeared to last at least two years after giving birth, the study found. Mothers who had the most pronounced alterations in their brains also scored higher on tests of emotional attachment to their babies than women whose brains underwent subtler changes.

"This study provides the first insights into the impact of pregnancy on the gray matter architecture of the human brain," said lead study author Elseline Hoekzema of the University of Leiden in The Netherlands.

While the exact cause of these shifts in the brain isn’t clear, it’s possible the changes may help women prepare for the social demands of motherhood, researchers report in the journal Nature Neuroscience.

For the study, researchers scanned the brains of 25 women who had never had babies, then did imaging tests again after the women gave birth for the first time.

Researchers also looked at brain scans from 19 first-time fathers, 17 men without children and 20 women who had never given birth.

Compared to the other participants, the first-time mothers had a distinct loss of gray matter in regions of the brain associated with what’s known as "theory of mind," or the ability to attribute mental states such as thoughts, feelings and intents to themselves and other people.

When researchers showed these first-time mothers pictures of their own babies, they had more activity in some of these pregnancy-altered brain regions than when they looked at images of other babies, the study also found.

Nearly all of the gray matter changes were still present in scans done two years after women delivered their babies. Some of the gray matter volume that was reduced during pregnancy returned in the hippocampus, a region associated with memory.

This pattern of structural changes was so consistent that it could be used to distinguish the brains of women who had given birth from those who had not, as well as to predict the quality of mothers’ attachment to their infants in the postpartum period, the researchers conclude.

Beyond its small size, limitations of the study include the lack of information about when or why changes in the brain might occur for first-time mothers.

It’s unclear if the changes in the mothers’ brains were caused by nine months of pregnancy, many hours of labor and delivery or by the first days and weeks of mother-infant bonding, said Dr. Rebecca Saxe, a neuroscience researcher at the Massachusetts Institute of Technology in Cambridge who wasn’t involved in the study.

The study also doesn’t tell us what happens in subsequent pregnancies, Saxe added by e-mail.

"This could be a once in a lifetime change, even if you have many more pregnancies,” Saxe said. "If so, we should be especially careful about making overly strong inferences about the link between neural changes and parent-infant bonding—since obviously, mothers do bond with later children."

Still, the findings add to a growing body of research documenting shifts in the brain associated with pregnancy and parenthood, said Dr. Mel Rutherford, a psychology researcher at McMaster University in Hamilton, Ontario, who wasn’t involved in the study.

Other research has found women may become more vigilant about strangers and develop a nesting instinct during pregnancy, both of which may be linked to changes in the brain, Rutherford said by e-mail.

"More generally, there is evidence of broader cognitive reorganization: Some cognitive processes become prioritized during the pregnancy, perhaps in service of protecting the investment in the pregnancy," Rutherford said.

SOURCE: Nature Neuroscience, online December 19, 2016.