"Our research suggests that psychological distress during the pregnancy period has a small but persistent effect on children’s risk for aggressive, disinhibited and impulsive behaviours," said Irene Tung from California State University - Dominguez Hills.

"These findings add to the evidence that providing widely accessible mental health care and support during pregnancy may be a critical step to help prevent childhood behaviour problems," Tung added.

For the study, published by the American Psychological Association in the journal Psychological Bulletin, the team analysed data from 55 studies with more than 45,000 total participants.

All the studies measured women's psychological distress during pregnancy (including stress, depression or anxiety) and then later measured their children's "externalising behaviours" -- mental health symptoms directed outward, such as attention deficit hyperactivity disorder or aggression.

Overall, the researchers found that women who reported more anxiety, depression or stress while pregnant were more likely to have children with more ADHD symptoms or who exhibited more difficulties with aggressive or hostile behaviour, as reported by parents or teachers.

They found that even after controlling for later (postnatal) psychological distress, distress during pregnancy in particular increased children’s risk of developing externalising problems.

The effect held true regardless of whether the children were boys or girls. And it held true for children in early childhood (ages 2-5), middle childhood (6-12) and adolescence (13-18), though the effect was strongest in early childhood.

The findings are consistent with theories that suggest that exposure to stress hormones in utero can affect children's brain development, according to the researchers.

Future research should focus on increasing diversity to understand the cultural and socioeconomic variables that affect prenatal stress and to develop effective interventions, according to Tung. IANS/KB