British Columbia

Mothers' stress from time of conception linked to stress at age 11

The SFU study was done by measuring cortisol — the stress hormone — over 12 years: starting with mothers before they were pregnant and ending with their 11-year-old children.

Stress testing was done over 12 years, beginning with mothers-to-be before they were pregnant

The SFU study was done by measuring cortisol in mothers-to-be, starting with their levels before they conceived and into the first eight weeks of their pregnancies. (Shutterstock)

A new study from researchers at Simon Fraser University has found mothers' stress levels when they become pregnant — and even before they conceive — is linked to the way their children respond to stressful situations later in childhood.

The study, published in the Journal of Developmental Origins of Health and Disease last month, also found that boys and girls were affected differently by strain their mothers experienced.

Pablo Nepomnaschy, an SFU health sciences professor who led the study, said the findings highlight a new challenge for society to tackle.

"Now we know that exposure affects development from conception or ... even before conception," he said.

"How are we going to protect our children-to-be, before they even exist?"

Study finds differences in boys, girls

The study was conducted over 12 years with a group of 22 mothers and their children in Guatemala, where Nepomnaschy had been working on a separate project.

Researchers measured cortisol in expectant mothers from before they were pregnant through the first eight weeks of their pregnancies. The team pinned down the day of conception and monitored stress levels with urine samples taken every other day.

Twelve years later, the research team tested their children and studied how they reacted to two different stressors: going back to school and taking a public speaking challenge.

The results, they found, differed between boys and girls.

SFU researchers chose two stressors for children in their study: one "natural" and one "experimental." Going back to school was the natural stressor. (Jonathan Hayward/Canadian Press)

The boys whose mothers were more strained in the second week of their pregnancies handled "known" stressors, like heading back to class, better than the girls.

The boys were, however, more stressed about the "trigger" challenge of public speaking.

Girls whose mothers had higher cortisol in the fifth week of their pregnancies were the other way around: stressed about returning to school but more relaxed with the public speaking.

That said, both boys and girls had higher general stress levels facing either scenarios if their mothers were under pressure at the fifth week of their pregnancy — the week the "stress" axis of the brain begins to form.

Nepomnaschy, who conducted the study with Dr. Katrina Salvante, said the gender divide is "extremely important" to note.

"It's very, very common to lump boys and girls together in these type of studies to increase sample sizes. But it seems here that early challenges affect boys and girls differently," he said.

"That's an important thing to do to study further."

SFU health sciences professor Pablo Nepomnaschy led an interdisciplinary research team for the study, which was conducted over 12 years. (Simon Fraser University)

Further examples found the way a child was affected by their mother's stress depends on the week she was stressed and what part of an embryo was developing at the time.

What's most important, he said, is that the findings show women of reproductive age need to be "really cared for" to keep stress low, whether or not they're planning a pregnancy.

"Most women do not know they are pregnant until they have been gestating an embryo and then a fetus for a few weeks," the associate professor said.

"So, any woman at any time who could be pregnant and not know it, she could be exposing her child-to-be to exposures that may affect the way that child will grow and develop and perform in life later on."

Nepomnaschy said the biological factors that create this link aren't clear yet, but genetics, epigenetics, environmental and cultural factors shared between a mother and her child play a role.

SFU's Faculty of Health Sciences and Statistics Department collaborated with the B.C. Children's Hospital Research Institute and the Department of Statistics at the University of Waterloo for the study.