Lack of reactivity to stressful events and depression during pregnancy can lead to poorer infant health, researchers have found.

The researchers,  including Co-author and study Principal Investigator Dr Mark Feinberg (Pennsylvania State University) and Co-author Dr Mike Roettger (ANU School of Demography), examined the real-time cortisol levels of 123 expecting mothers between 12 and 32 weeks pregnant.

Cortisol is a hormone that is produced when the body is under stress and triggers the fight or flight response to perceived threats of danger. 

But in cases such as chronic anxiety or depression, cortisol levels may not increase in response to stress.

The researchers found mothers whose cortisol levels did not change in response to stress had children with significantly worse health outcomes in the first three years of life.     

For example, mothers who had minimal cortisol reactivity to stress had children with double the amount of GP visits than children of mothers who did react to stress.

In addition, their children were three times more likely to have respiratory infections, colds, fevers, and ear infections during the first three years of life.

Poorer child health was also found to be more likely when expectant mothers had reported higher levels of depression.

The researchers say it can be unavoidable to experience stress but it is important to manage it, particularly during pregnancy.

"Feeling and responding to stress is natural, but if stress lingers or pregnant women are feeling chronically depressed or anxious then they need to seek help and go to their obstetrician or GP," Dr Roettger said. 

"These results suggest that effective treatment may positively benefit both mothers and their child's health in the first years of life."

Co-author and study Principal Investigator Dr Mark Feinberg, from The Pennsylvania State University said: "Even better, is to prevent high levels of stress and depression in pregnancy.

"We've been focused on preventing these problems in the first place in developing the Family Foundations program for expectant couples."

The study results are published in Psychosomatic Medicine.

"This is the first study of its kind to look at how child health is linked to expectant mothers' cortisol levels in response to a typical stressor in the home. We used a common stressor - a conflict discussion with a partner - to measure the responsiveness to stress," said Dr Roettger.

"Cortisol levels tend to be less reactive with people are depressed. Other factors such as prenatal anxiety or chronic stressors may produce similar results.

"We found expecting mothers who had low levels of cortisol reactivity to relationship stress gave birth to children who had more ear infections, fevers and colds and needed more doctor visits."

The study adds to current research linking maternal stress and child health, including low birth weight, delayed development and baby brain development.

"For doctors and health care professionals looking at this research, it provides an added incentive to prevent or treat prenatal depression or anxiety," said Dr Roettger.

"There is so much awareness about avoiding alcohol, smoking, and substance use during pregnancy, but effectively managing stress and mental health is important too.