ASk A Researcher

April 2014

Stress effects on pregnancy: The impact of the 2009 Red River flood on birth weight

Clayton Hilmert is a health psychologist in the NDSU Department of Psychology. His primary interests are in stress, cardiovascular health, and pregnancy. Current research involves the effects of stress in the natural environment on pregnancy, the effects of social support on stress and health, and associations between how a person responds to stress biologically and the emotions the person experiences.




Q: Why is low birth weight important?

In general, babies who are born lower birth weight, especially those less than 2,500g (about 5.5lbs) are at significantly greater risk of a number of health problems in infancy including respiratory distress, bleeding on the brain, developmental issues including inhibited growth and cognitive development, and disease in adulthood including high blood pressure and diabetes. Low birth weight is also associated with greater rates of infant mortality.

About 8% of babies born in the United States are low birth weight (<2,500g). That’s about 1 in every 12 newborns. Even with our increased knowledge concerning low birth weight and our efforts to reduce the number of babies born low birth weight, this rate has remained steady for years. So this is a serious condition for many reasons.

Q: How does stress tie into low birth weight?

As I mentioned, even with a better understanding of the importance of prenatal healthcare, proper nutrition and diet, and the dangers of smoking, we still have a steady 8% rate of low birth weight childbirths. That is to say, prenatal care, nutrition, and quitting smoking have made significant improvements in the health of our newborns, but we still have a relatively high and steady rate of these adverse birth outcomes that is not addressed by these issues. In addition, there are some groups, particularly African-Americans, who have low birth weight babies 2-3 times as often as other races. This is where stress comes in to the picture.

Recently researchers have starting looking at how stress during pregnancy may contribute to when a child is born, or the length of gestation, and the growth of the fetus, both of which determine a baby’s birth weight. And so far, this research has been very informative.

Different kinds of stress, including living in a stressful environment (e.g., a neighborhood with high crime and few healthy resources), feeling like you don’t have control in your life, having high anxiety, being depressed, and worrying too much about the pregnancy have been associated with giving birth to lower birth weight babies. Even when we account for prenatal care, nutrition, and health-related behaviors (like smoking and drinking, perhaps because someone is stressed), stress by itself still predicts babies’ birth weights. In addition, lacking the resources to cope with stress, particularly not having supportive family or friends around you has been associated with lower birth weight.

Q:What are some of the biological ramifications of stress on the body of the mother? The child?

The biology of pregnancy is fascinating. The way a body adjusts so that the growth of a fetus can be accommodated is in many ways elegant and harmonious. But these adjustments require a balance between the mother’s regular biological functioning and that of the fetus and placenta. Some of this balancing act involves the regulation of certain hormones that are produced by the mother and by the placenta. Also, the mother’s cardiovascular system has to produce more blood and work harder to circulate blood to the mother and fetus.
Interestingly the hormones and cardiovascular parameters that adjust for pregnancy are also intimately involved with how a body responds to stress. That is, when someone including a pregnant woman gets stressed, these same hormones (e.g., cortisol) balanced for pregnancy increase. Also, stress tends to cause increases in blood pressure. These biological reactions to stress are known as the “fight-or-flight response” that we all experience when we are stressed.

Considering these shared biological links with stress and pregnancy, you can see how the elegant, harmonious balance of hormones and blood pressure during pregnancy might be more difficult to sustain when a pregnant woman is stressed. Although we are still learning exactly how these disruptions in balance are associated with low birth weight and other adverse pregnancy outcomes, it seems clear that the effects stress has on hormones and blood pressure are related to how stress “gets under the skin” of a mother and affects the baby’s birth weight.

Q: Do these effects vary based on stage of pregnancy?

Another interesting effect of stress on pregnancy was first reported by my colleagues in California who studied the impact of experiencing a serious earthquake during pregnancy. In this study it was found that women who went through this very stressful event during their first trimester said they were more stressed by the earthquake and gave birth earlier in their pregnancies than women who experienced the same earthquake later in pregnancy. This and other studies suggest that as pregnancy progresses the mother becomes less sensitive to stressful events and stressful events have less impact on pregnancy outcomes. This may be a natural defense that develops, protecting the mother and fetus the further along they are in pregnancy.

Q: How does this tie in to your research on the effects of the 2009 Fargo flood?

In March 2009, when a new report came out almost every day saying that the flood was going to be worse than it said it would be yesterday, I was still a new professor and had great colleagues that kept asking if I was going to do any stress research. Although it was a lot of hard work for me and, needless to say, a little stressful at times, with the help of excellent students at NDSU, who made it all possible, we carried out a study of pregnancy and stress during the record-breaking flood of 2009 with the help of Sanford (then Meritcare) and Essentia (then Innovis) OB/GYN departments. Within a trimester of the flood crest on March 28, we had almost 200 pregnant women provide us with information about the stress they experienced and the activities they undertook during the flood.

What we found, was mostly what we expected, women who lived closer to flood and evacuation areas (and who were presumably more stressed about the flood than those further away) tended to give birth to smaller babies. This was especially true for women who were closer to flooding areas and in their first or early second trimester. What we also found was that it didn’t matter whether a pregnant women lifted and placed sandbags, packed up valuables and evacuated, or rested in her home while her family and community worked to hold back the flood; the effect of the stress of the flood on birth weight was still evident.

There are a lot of reasons why this research is important. First, it further supports the idea that “real world” stress, not just stress on a survey or in a laboratory, has a significant impact on pregnancy and birth weight. Also, our study supports other research showing that the impact of stress seems to decrease as pregnancy progresses. Lastly, flooding is the most commonly experienced natural disaster on earth. While this may not seem so surprising to us eastern North Dakotans, we still need to realize that during the flood of 2009, all of our study participants were receiving excellent prenatal care from local health care institutions and there were very few babies born less than 2,500g. However, areas where flooding occurs frequently in other parts of the world may not be blessed with the type of infrastructure and healthcare available to us here. It makes me wonder how the stress of a major flood impacts the pregnancies of women who are already at risk of having less healthy babies.

Q: What can we do to avoid the adverse effects of stress on pregnancy outcomes?

First, it’s easy to say, “Don’t sweat the small stuff,” but that’s not always easy to do, especially when it’s not small stuff that’s making you stress (like a record-breaking flood). But learning not to react excessively to less significant things (like losing your keys, being late for an appointment) is important to mitigating the effects of stress on health. For most of us this takes work. There are a number of different techniques a person can learn to avoid excessive reactions and to quickly calm themselves down if they do start to “freak out.” For instance, there are specific relaxation techniques, physical activity helps some people, others like to do something called Mindfulness Based Stress Reduction, which is relatively new to us and showing much promise. You can ask your physician for some recommendations, I know hospitals in the area have some excellent resources along these lines.

Another big component of avoiding the negative impact of stress is social support. If you have positive people around you to help you when you need help and to just be there when you need someone there, research shows that this has a robust positive effect on health. So this message is not only for those who want to avoid stress, but also for those who want to help others avoid stress. You can be a key factor in helping your pregnant wife, friend, or family member avoid the negative impacts stress can have on a pregnancy by being there for them.


The March of Dimes website ( has some excellent resources for information on pregnancy including a peristats generator that provides many different statistics on pregnancy outcomes (

Glynn, L. M., Wadhwa, P. D., Dunkel-Schetter, C., Chicz-Demet, A., & Sandman, C. A. (2001). When stress happens matters: effects of earthquake timing on stress responsivity in pregnancy. American Journal of Obstetrics and Gynecology, 184(4), 637-642.

For more information on natural disaster rates all over the world, visit EM-DAT: The OFDA/CRED International Disaster Database – Université Catholique de Louvain, Brussels (Belgium).

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