Typically, levels of the stress hormone cortisol are high when you wake up in the morning and decline through the day. But some people have a low cortisol level in the morning, and a smaller-than-normal decline during the day, the study authors said.
That abnormal pattern -- associated with chronic stress and a history of trauma -- has been linked to progression of a number of diseases, including cancer and hardening of the arteries, the researchers said.
It may also predict the weight of your baby.
"We found that the same cortisol pattern that has been linked with chronic stress is associated with delivering a baby that weighs less at birth," study author Christine Guardino, a postdoctoral scholar in psychology at the University of California, Los Angeles, said in a university news release.
She and her colleagues looked at 142 pregnant woman in Baltimore; eastern North Carolina; Lake County, Ill.; Los Angeles and Washington, D.C.
To assess the women's stress levels, the researchers analyzed blood pressure, body mass index, cortisol levels in their saliva and other factors.
The study, published online recently in the journal Health Psychology, suggests a mother's cortisol patterns before pregnancy affect a baby's birth weight.
Each year, more than 300,000 babies with a low birth weight -- less than about five-and-a-half pounds -- are born in the United States. These babies are at increased risk for health problems and even death.
Elevated levels of cortisol in mothers lowers blood flow to the fetus, reducing the supply of oxygen and nutrients, said study co-lead author Chris Dunkel Schetter, a professor of psychology at UCLA.
Women planning to become pregnant should assess their stress levels and take measures to reduce them if necessary, the researchers said.
"Improving pre-conception health can profoundly improve our overall health," Dunkel Schetter said in the news release.
"Women should treat depression, evaluate and treat stress, be sure they are in a healthy relationship, be physically active, stop smoking and gather family support. All of the things that create an optimal pregnancy and healthy life for the mother should be done before getting pregnant," she advised.
The U.S. Office of Disease Prevention and Health Promotion offers tips for a healthy pregnancy.
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