Children whose mothers lived through stressful events during pregnancy are more likely to have behavioural issues later in life, according to a new study led by a researcher at the University of Ottawa.

Ian Colman, an associate professor with the faculty of medicine, and his team examined responses given by mothers when they were 18 weeks pregnant as to whether they were going through highly stressful events such as a family death or illness, or a partner's job loss.

Ian-Colman

Ian Colman is Canada research chair in mental health epidemiology at the University of Ottawa. (University of Ottawa)

They then looked at how the children born from those pregnancies behaved between the ages of six and 16.

The research team found mothers exposed to the highest levels of prenatal stress were more likely to have children who suffered from either hyperactivity or a "conduct disorder" — a pattern of behaviour where children may be aggressive, refuse to follow rules or overstep social norms.

"We're looking at very objective, specific stressful events that are happening in the environment around them," Colman told CBC Radio's All In a Day Wednesday.

"We're not just asking, 'Are you feeling very stressed today?'" 

Cortisol to blame?

The research looked at data taken from the Avon Longitudinal Study of Parents and Children, which has been following the lives of approximately 14,500 people born in the 1990s in the United Kingdom.

It was recently published in the journal Biological Psychiatry.

Colman said that the hormone cortisol and its affect on the fetal brain could potentially explain the link between stressful pregnancies and later behavioural problems.

'The most important thing is surrounding yourself with a supportive network.' - Ian Colman

"We know that when a mother is stressed, there's a lot of cortisol running through her body. And we know that cortisol can pass the placental barrier and affect the developing fetus," Colman said.

"That increases the level of cortisol for the fetus, and also levels of testosterone in the fetus. That testosterone gets carried on into childhood, and testosterone is associated with aggressive behaviour."

Since it's normally impossible to avoid an event such as a family member's death, Colman said there are ways pregnant mothers can keep their stress levels low.

"If possible, do less. Keep your tasks manageable. Do things like try to be physically active. Do yoga or meditate, if you find that helpful," he said.

"But the most important thing is surrounding yourself with a supportive network, so you can talk to your loved ones about stress that you're feeling. And then hopefully, they can help you manage that stress as well."

Preliminary research also suggests raising a child in a supportive environment can undo some of the effects of prenatal stress, Colman added.