Fetuses know when their mothers experience toxic stress, experts say

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There's stress and then there's toxic stress — that feeling of being chronically overwhelmed, anxious, or depressed. Catherine Monk, Ph.D. studies the effect this kind of stress has on babies before they're born. She sat down with KPCC's early childhood reporter Devin Browne to explain more.

What’s the difference between stress and toxic stress? Is it just a matter of degree?

It’s degree, but it’s also what’s contributing to the stress. We all have stress about getting an assignment done for work or school, going in front of an audience in some way — life is challenging. There are stressors in it. Toxic stress, though, tends to be threats to our self and our self-integrity, either from domestic violence or from not knowing where our next meal is coming from, housing insecurities, past abuse that’s never been resolved, very acrimonious relationships – so that if we’re pregnant, we’re not sure where the support is going to come from for our child, really unresolvable tensions between work and demands at home. It’s usually chronic and can take the form of depression or anxiety or both.

Your research is about the relationship between maternal toxic stress and fetal behavior. What exactly are you trying to find out?

What we’ve done is recruit women who reflect the range of experiences in pregnancy, so some of them are having this toxic stress — they’re very depressed, they’re not getting treatment. And then others are having the more average [experience of] "life has ups and downs and I’m doing OK." We have the women come into our lab and give them just a very small stressor test, because we want to get them in the moment feeling that (gulp!) fight or flight response. Then we look at what fetuses do when there’s that kind of perturbation to their in utero environment associated with just their mother’s mental experience—I’m being asked to do a cognitive challenge in this lab test, I’m feeling a little stressed—and what we’re seeing is that the fetuses that have been exposed throughout pregnancy to this toxic stress are more reactive to their heart rate changes than they are to other fetuses whose mothers are not exposing them to that kind of toxic stress because they’re doing better in their lives.

So this is very important because there’s been literature going back to the Barker hypothesis—that’s the hypothesis that says there are developmental origins of diseases, meaning that some can start in utero—and this hypothesis has been supported by epidemiological data showing that nutrition and stress in pregnancy are associated with long term health outcomes in adults. So for example, the Dutch famine that happened right after World War II was not only an example of a caloric reduction for women while they’re pregnant, but unbelievable stress to not know where your next meal is coming from because of an embargo on food getting into the Netherlands. Babies who are in utero in the couple of months of this famine—male babies—went on to have greater risks of being schizophrenic, of having a very serious mental disorder. So really now there have been hundreds of studies making this association that toxic stress in pregnancy can put the future child at risk for mental disorders. One of the other strong, strong findings is anxiety during pregnancy and children having a greater risk factor for Attention Deficit Disorder. So we wanted to contribute to this science by identifying the effect of maternal toxic stress at the time it’s occurring, so on the fetus. [This] can really add to the science by removing the post-natal influences that are also there.

And you’re finding that mothers who are experiencing toxic stress are probably going to have babies who have a higher likelihood of developing certain disorders later on in life?

Probably is probably too strong. We tend to be rather conservative as scientists and particularly in this case, we need to be. The factors that have shaped who you and I are are a multitude: They’re our grade school teacher, they’re our cousins, they’re the air we breathe, the air our mothers breathed during pregnancy, other kinds of chemicals she may have been exposed to, siblings, parents, aunts—there are so many factors. But what we are saying is that when there is toxic stress in pregnancy—that really severe kind of stress—it is a factor contributing to risk for these brain behavior problems as a child. And most importantly, it’s a preventable risk factor.

How can it be prevented? What are you finding that’s working in terms of mitigating toxic stress?

We do know how to help women with their toxic stress experiences and a lot of times, I say that and people look at me like I’m crazy, because some of toxic stress comes from socio-economic factors and those can feel very challenging to solve. I’m not trying to claim that we can easily solve those. But what we can do is we can help how women—and this is true of cognitive behavioral interventions in general—with managing what life is giving to them. So we can, as we’re doing in my lab right now, have an intervention, where we work with women before the baby’s born, providing tools that can really support them in their caregiving, so they can be the best caregiver possible. We’ve developed called “Practical Resources for Effective Post-Partum Parenting, which is a coaching approach to helping women. Importantly, these behavioral interventions are added to their OB visits. We really don’t want to burden women with more sessions to go to; we want to make it easy for them. It’s a four-session intervention. Part of what goes on with this coach is the one-on-one actualization of support and then we’re talking about their other resources for support, what their lives are like. We’re giving them mindfulness so that they can slow down, use sensory skills to pause when there’s a lot of stress, to check in with their own emotions, to be able to reflect on how important support feels, from what they get with their coach, thinking about how they can get it in their lives. And then we do this big part of giving them different behavioral tools with their future baby around how to regulate the baby, so day and night cues, how to swaddle, and also psycho-education: what to expect when their baby comes, how much crying because we all do better when we feel in control when we can anticipate.

What’s your next big research question?

We still want to understand how a mood state like I am feeling overwhelmed in my life—how does that get to the fetus and get under the fetus’s skin to shape their behavior and their brain development? We have one paper we published recently showing that a gene in the placenta produces an enzyme that deactivates the stress hormone cortisol as it crosses into the placenta from the mother. And we’ve shown that when there’s more toxic stress in pregnancy that gene is turned off through an epigenetic process and that’s very important. It gets us closer to understanding the biological pathway of how a mood and emotion could get under the baby’s skin in utero to affect their development. So we really want to learn more about the placenta and how its functioning may be altered based on maternal stress, and really getting at what’s called the molecular basis of genes getting turned on and turned off that may influence brain development before [babies] are born.

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