​Toronto, Nov 16 (IANS) Depressive symptoms in women during and after pregnancy are linked to reduced thickness of the cortex -- the outer layer of the brain responsible for complex thought and behaviour -- in preschool-age kids, says a new study.

"Our findings underscore the importance of monitoring and supporting mental health in mothers not just in the post-partum period, but also during pregnancy," said lead researcher Catherine Lebel of the University of Calgary in Alberta, Canada.

The findings, published in the journal Biological Psychiatry, suggest that a mother's mood may affect her child's brain development at critical stages in life.

Eighteen percent of women experience depression some time during pregnancy, and both peri-natal and post-partum depression have been associated with negative outcomes in children. 

But the associations between maternal depression and abnormal brain structure in kids at this age was not known.

For the study, the researchers screened 52 women for depressive symptoms during each trimester of pregnancy and a few months after the child was born. 

The women ranged in the presence of symptoms, some with no or few symptoms, and some meeting the screening criteria for depression. 

When the children reached about 2.5 to 5 years of age, the researchers used magnetic resonance imaging (MRI) to measure their brain structure.

Women with higher depressive symptoms tended to have children with thinner frontal and temporal areas, cortical regions implicated in tasks involving inhibition and attention control.

The researchers also found an association between depressive symptoms and abnormal white matter in the frontal area, the fiber tracts connecting the region to other areas in the brain.

These associations were only found when symptoms occurred during the second trimester and post-partum, suggesting these periods are particularly critical times for child brain development.

Abnormalities in brain structure during critical periods in development have often been associated with negative outcomes, such as learning disabilities and behavioural disorders, the researchers said.