Daughters born to women with high levels of cortisol -- a stress hormone -- during pregnancy could be at an increased risk of developing anxious and depressive-like behaviours by the age of two, a new study has reported.

The effect of elevated maternal cortisol appeared to result from patterns of stronger communication between brain regions important for sensory and emotion processing. It could be because maternal stress may alter connectivity in amygdala -- a brain region important for emotion processing -- in the developing foetus, suggesting that vulnerability for developing a mood disorder is programmed from birth.

This could be an early point at which the risk for common psychiatric disorders begins to differ in males and females, the researchers explained. "Higher maternal cortisol during pregnancy was linked to alterations in the newborns' functional brain connectivity, affecting how different brain regions can communicate with each other," said Claudia Buss from Charite University Medicine Berlin in Germany.

"Many mood and anxiety disorders are approximately twice as common in females as in males. The study highlights one unexpected sex-specific risk factor for mood and anxiety disorders in females," said John Krystal, Editor of Biological Psychiatry, in which the study is published.

Conversely, sons born to mothers with high cortisol during pregnancy did not demonstrate the stronger brain connectivity, or an association between maternal cortisol and mood symptoms, the researchers said. For the study, the team measured cortisol levels over multiple days in early, mid and late pregnancy. Measurements taken from nearly 100 mothers reflected typical variation in maternal cortisol levels. The researchers then used brain imaging to examine connectivity in the newborns soon after birth, before the external environment had begun shaping brain development, and measured infant anxious and depressive-like behaviours at two years of age.