The stress and level of hardship faced by pregnant women during the 1998 Quebec ice storm may have affected the health of the children they gave birth to, researchers say.

In Quebec, the ice storm caused widespread power outages and millions of people went without power for long periods after heavy ice toppled power pylons.

Scientists from the Douglas Mental Health University Institute and McGill University have been following a group of 150 families in which the mother was pregnant during the natural disaster. They found that the number of days a woman went without electricity influenced the genetic expression of her child.

In 36 of the children examined, researchers found the DNA inside a type of immune system cell called a T cell was modified. They say this type of DNA modification, called methylation, affects how genes are expressed.

The health effects of the change in genetic expression aren't clear, but researchers say it could put children at a greater risk to develop asthma, diabetes or obesity.

The goal of the study was to see if maternal stress affects the health of children. One of the researchers involved, McGill University pharmacology and therapeutics professor Moshe Szyf, says researchers haven't been able to examine this before. 

"We have evidence in animals that if you stress an animal during the pregnancy that will have long-term effects in the way the DNA is programmed and the way their health shapes up later in life. But we didn't know if this can happen in humans … because it's unethical to stress little babies," he says.

Szyf says this study is the first to show that objective stress, such as the number of days a woman went without electricity, is what causes long-lasting changes in genetic expression and not the degree of emotional stress.

Results of this study have been published in the international online publication Plos One this month. 

Szyf says the research need to be replicated in a larger study, but that it highlights how important it is to keep a non-stressful environment for pregnant women.