Stress and the Placenta

Why our social environment matters

Journal: Obstetrics and Gynecology Clinics of North America
Date: March 2020

At the moment of fertilization, an embryo immediately begins sensing for nutrients in the surrounding environment. As it makes its way to the womb, big structural changes are already occurring in order to create the only organ to last just nine months: the placenta. Once the fertilized egg embeds itself into the uterine wall, the placenta begins to immediately send out roots that find and reshape blood vessels in the womb, seeking to connect itself to the mother and invade her arteries for nutrients that will help it grow, mature and nurture the new fetus 

Within those nine months, the placenta provides all of the nutrient building blocks to create a new human being. Yet we actually know very little about it. It’s usually an afterthought – the afterbirth – something discarded and forgotten about. It turns out that growing an entire organ during pregnancy   reveals a lot more than we previously knew. Most importantly, it determines how well the baby grows and is nourished. But more than that, there are numerous factors that help or hinder its ability to do its job – and many of these are related to the social environment of the mother. 

A 2020 journal article titled Social Determinants of Placental Health and Future Disease Risks for Babies, the authors propose that the social conditions a mother experiences before and during pregnancy affect the developing baby by way of the placenta. Their whole premise is that the placenta is far more affected by a woman’s social environment than we thought, and therefore the health of her baby - and future generations - are too. We’re learning that the placenta is exquisitely sensitive to everything happening in a woman’s life - from her nutritional status, to her relationships, economic status, chemical exposures and psychological state of mind. In short, her stress levels. 

Mom’s environment is society. Where she lives, plays, gets her food, and where she goes to work and school. How a mother thrives determines how her baby thrives – and we all want the best for our babies. All human beings should have nutrient-rich diets, low stress levels, economic stability, clean air to breathe and clean water to drink. This is especially important for pregnant women, because their health and well-being determines the health and well-being of future generations.  

 But that’s not the reality for an untold number of women. The social stresses many women face during pregnancy include poverty, lack of social support, domestic violence, racism, misogyny, housing insecurity, crime, environmental pollution and hunger. What happens when mothers lack the social and physical support they need? They suffer. This means their babies suffer too, and their growth, development and long-term health are compromised because of it.   

When a mother is stressed, she releases the well-known hormone cortisol. Cortisol stimulates the placenta to increase production of its own stress hormone, which rises in step with mom’s cortisol production. Nature does have a built-in protection, however. The placenta has the ability to chemically neutralize cortisol to its inactive form, called cortisone. However, this protective mechanism can get overwhelmed under extremely stressful conditions. When this happens, cortisol makes its way through the placenta to the baby. Cortisol inhibits fetal growth, so even babies born at full term to highly stressed mothers can be small. We know that babies who are born at the low end of the birthweight scale have a higher risk for developing heart disease, type 2 diabetes, obesity and other diseases later in life.  

In addition to cortisol, environmental contaminants can cross the placenta and cause problems. These exposures are responsible in part for preterm births because the placenta’s protective mechanisms get overwhelmed and compromised by inflammatory processes. Chemicals in cigarette smoke, heavy metals, fine particulates in the air, plasticizers, pesticides and other contaminants do more damage when they are combined with high stress levels – something called a synergistic effect. 

Toxic stress also contributes to several medical conditions that can lead to placental abnormalities. Conditions like maternal obesity, gestational diabetes, preeclampsia and a disturbed maternal microbiome. The microbiome, an ecosystem of some 100 trillion microorganisms living in our intestines, plays a large role in physical and mental health. A mother’s microbiome can be diminished by a number of stressors, which in turn affects her digestion and the transfer of beneficial bacteria to her baby.  

Over the last three generations, the health of the US population has worsened. We’ve become more vulnerable to diseases like heart disease, type 2 diabetes and obesity. What is behind this trend? Social factors known as the social determinants of health. They include things like social and community context, economic stability, the built environment, educational attainment, and health and health care. All of these are largely determined by where you live – in other words, your zip code. Not having access to these basic needs creates a chronic stress response with direct biological implications. Social stressors contribute to the diseases we mentioned above, in very pervasive ways. Think of all the pregnant women in our society who are experiencing toxic levels of stress, and how this epidemic of stress is harming not only this generation, but the future health of our society.   

Many social determinants of health overlap and intersect. Let’s look at five of them, through the lens of a pregnant woman:

  • Social Context: This is critical for a pregnant woman’s well-being. It can include the support network she has, whether she has child care for her other children, if she’s in a healthy relationship with the father and others, and if she’s experiencing injustices like violence, racism, misogyny and crime. Feeling unsafe and unprotected while pregnant is extremely stressful. This can be an exceptionally vulnerable time in a woman’s life.  

  • Economic stability: This translates directly into things like where you can afford to live, what food you have access to, whether you have transportation options or if you can take sick days. When a pregnant woman has limited income and financial support, she may have a limited food budget, and be more likely to eat low-cost, processed foods. Fresh, whole foods may be unavailable or too expensive. We know that poverty and obesity are linked - and maternal obesity is associated with gestational diabetes, preeclampsia and cesarean sections. Maternal obesity also affects placental growth and function, and puts the developing baby at higher risk of childhood obesity and carries other metabolic and behavioral consequences. 

  • The built environment: Where she lives can determine whether a mother is exposed to toxic pollutants, and the quality of air and water she has. It determines where and how she gets her food, the quality of her food and whether it’s safe to exercise outdoors and maintain healthy social connections with people in the community. It also determines her exposure to the stressors of crime, violence, excess noise, trash and having to be on guard for fear of being violated.  

  • Education: A mother’s level and quality of education intersects with her economic stability, health, social context and built environment. Lacking basic knowledge or the ability to reason and be self-aware are tied in with educational attainment and the kinds of social skills that improve health. Studies show that higher academic achievement is associated with increased health behaviors and lowered risk behaviors. We also know the more educated a woman is, the healthier her children are likely to be.  

  • Health and healthcare: Health is more than just the absence of disease. Outside of the health care system, policies that promote health and health equity make the biggest improvements in community-wide health. Within the health care system, it means having access to culturally appropriate, affordable and timely pre- and post-natal care, as well as to a pediatrician or family care.  

There is a clear link between the social environment, a woman’s health, her placental function, her baby’s health and the health of future generations. The authors of this journal article make the case that evaluating a baby’s risk for future disease should also include an assessment of the social context of a woman’s pregnancy. Although most of the effects of toxic stress on a baby’s health haven’t been investigated, there is enough evidence to suggest that these exposures and interactions warrant further study and that more investment is needed into policies that improve the social determinants of health for women. 

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The OHSU Bob and Charlee Moore Institute for Nutrition & Wellness supports human research that seeks to find the links between maternal stresses, including poor nutrition, and elevated disease risks for babies as they become adolescents and adults. 

Thornburg K., Boone-Heinonen J., Valent A., (2020). Social Determinants of Placental
Health and Future Disease Risks for Babies, Obstetrics and Gynecology Clinics of North America. 47(1), 1-15.