Parenting kids is not exactly a low-stress job. In fact, it’s more anxiety-inducing now than it has ever been before. New moms in particular have to learn how to handle new stressors, all while raising a baby for the first time — so we have to wonder, how does stress impact how new moms parent?

In a new study published in Psychoneuroendocrinology, researchers found that a high concentration of cortisol in new moms is associated with greater intrusive parenting behaviors, and reduced brain activation to an infant’s cry in the motor planning and auditory processing regions.

Basically, moms who were more stressed let their babies guide their own play less, and were less responsive to their cries.

Ok, that was a lot. Let’s start from the beginning.

Coritsol is commonly referred to as the “stress hormone,” and naturally fluctuates throughout the day. It plays lots of important roles in the body, like regulating immune function and anti-inflammatory mechanisms, and dictating our fight-or-flight response.

Stress causes a rise in cortisol levels, but they tend to return to normal quickly. (Despite what you might see on TikTok, too-high cortisol levels, a symptom of Cushing syndrome, are quite rare, and a healthy baseline can vary from person to person).

High basal cortisol levels have, however, been associated with less engaged parenting behaviors, according to the study. Researchers have shown previously that, for moms of infants aged 3–6 months, higher basal cortisol levels were associated with less sensitive and more intrusive caregiving behaviors.

“Maternal intrusiveness refers to the degree to which the mother follows the child’s lead and waits for non-interruptive ports of entry into the interaction,” the study explained.

The researcher’s goal was to find out how cortisol might alter how mom’s brains function, and and to explain why and how that change translates to their parenting behaviors.

“The goal of this research was to understand how the multiple biological systems that underpin parenting behavior interact,” said study author Andrew Erhart. Erhart is the School Age Systems Specialist at the Colorado Department of Public Health and Environment, and conducted the research while a member of the University of Denver’s Family & Child Neuroscience Lab.

“We know that the transition to parenthood is a critical period where brain and body change to support the development of parenting behaviors. I am particularly interested in understanding how environmental influences like the postpartum environment and chronic stress moderate the biological changes in the transition to parenthood.”

The study looked at 59 first-time moms with infants aged 3 to 4 months. These moms attended home and lab-based sessions, where the researchers assessed their cortisol levels, behavior during interactions with their infants, and brain responses to infant cries.

At home, the researchers observed interactions, without using toys, between the moms and their babies. They then coded the behavior for sensitivity to the baby’s cues and non-intrusiveness. The researchers collected cortisol samples over the course of the session to determine the mothers’ average cortisol concentration.

In the lab session, the moms underwent functional magnetic resonance imaging (fMRI) scans. Researchers played recordings of the mother’s own baby, and a control baby, crying. They then used the fMRI scans to measure activity in different areas of the brain in response to the infants’ cries.

The home visits revealed a clear association between mothers with higher cortisol levels, or higher stress, and intrusive parenting.

The fMRI scans also revealed that higher cortisol correlated with decreased brain activity in response to the baby’s cries across multiple regions of the brain. This reduction in brain activity, linked to more intrusive parenting, led the researchers to conclude that moms with higher cortisol levels may have an impaired ability to respond calmly and effectively to her distressed baby.

The researchers were surprised, however, that the impact on the brain was focused more in areas of motor planning and auditory processing, rather than emotional regulation. Further research is needed to understand the connections between brain function and behavior involved in this process.

“The take-away point is that we have a better understanding of how our stress system interacts with the maternal brain when responding to infant cry, and how this relates to parenting behavior,” Erhart said. “We know that brain areas responsible for motor planning and auditory processing are the ones that are less engaged with greater cortisol concentration.”