High stress during pregnancy linked to increased cortisol in toddlers’ hair

Researchers from Washington University in St. Louis and Dartmouth College have discovered a link between cortisol levels in toddlers’ hair (a biomarker of long-term stress) and prenatal depression in the mother.

The findings, published in the American Journal of Human Biologysuggest that a child’s physiology under prolonged stress — or how the body responds to stress — may be influenced by conditions that occur in the womb, said study co-author Theresa Gildner, an assistant professor of biological anthropology in the arts and sciences at WashU.

The findings also highlight the potential of hair cortisol – a minimally invasive and easy-to-collect measure – to assess cortisol activity in infants and toddlers.

“Hair cortisol testing is less invasive than blood testing, the standard cortisol measurement technique, and more useful than saliva testing, which only reflects short-term changes in cortisol. With 1 centimeter of hair representing approximately one month of cortisol intake, hair cortisol testing can quantify cumulative cortisol exposure over longer periods of time,” Gildner said.

According to Gildner, the study was conducted primarily for research purposes, but it also has potential clinical applications.

“By understanding the long-term effects of maternal stress on her offspring and when these effects are most pronounced during pregnancy, we can better determine when interventions to support parents and reduce stress are most needed, and the potential long-term benefits of investing in these types of interventions to support both mother and child well-being,” Gildner said.

How Maternal Cortisol Affects Offspring

The hypothalamic pituitary adrenal (HPA) axis is the body’s system for dealing with stress. When the body experiences stress, the HPA axis releases a steroid hormone called cortisol. Cortisol levels naturally fluctuate throughout the day and in response to stress, but generally drop once the threat has passed.

However, chronic stress can disrupt HPA axis activity, keeping cortisol levels elevated. This can lead to serious health problems, including metabolic disorders, immune system dysfunction, increased inflammation, cancer, and mental illness.

During pregnancy, cortisol easily crosses the placenta. When a pregnant person’s cortisol level remains high, it can also harm the fetus and affect its development, including the fetal growth rate.

“Changes in offspring cortisol levels could potentially be beneficial, potentially leading to accelerated growth and development in response to early adversity. Essentially, the baby in the womb is receiving signals from the mother that the outside world is stressful, and their growth patterns can adapt in response,” Gildner said.

“However, these changes can also have negative consequences for the child, such as lower birth weight and problems later in life, such as increased behavioral problems and an increased risk of developing cortisol-associated health problems, such as depression, anxiety, digestive problems and weight gain.”

Interestingly, maternal depression did not have the same long-term impact on mothers. The researchers also tested maternal cortisol production 15 months after birth, but they did not find the same association. They also found no association between postnatal depression and offspring cortisol levels, suggesting that only direct exposure during pregnancy affected the offspring.

The current study was a relatively small one of 46 mothers and 40 toddlers, average age 15 months, but the results are encouraging. Gildner said they hope to build on this study, recruit a larger sample and continue the testing later in life.

“This may help us understand how long the effects of exposure to depression in mothers last in the womb,” Gildner said.