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updated 3/14/2011 2:57:51 PM ET 2011-03-14T18:57:51

The children of women who experience a stressful life event either during or before pregnancy are at an increased risk of being hospitalized from infectious disease, according to a new study.

Children whose mothers experienced a stressful event, such as the death of a loved one or divorce, while they were pregnant were 71 percent more likely to be hospitalized with a severe infectious disease than children of women who did not undergo prenatal stress, said study researcher Nete Munk Nielsen, an epidemiologist at Statens Serum Institute in Denmark.

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And the children of women who experienced a stressful life event 11 months before conception were 42 percent more likely to be hospitalized with severe infectious disease than the children of stress-free women, Nielsen said.

"We speculate that this is due to effects of longer-lasting stress following the stressful life event," Nielsen told MyHealthNewsDaily.

The study was published online last week in the American Journal of Epidemiology.

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Increased infection risks
Researchers looked at the health data for 1,670,269 Danish children born between 1977 and 2004, and asked their mothers if they experienced the death of a spouse or a child, or had gotten a divorce before or during pregnancy. The children were followed from four weeks after birth until they turned 15.

Researchers chose to measure stress by these events because "death of a spouse, death of a child and divorce are considered some of the most devastating and stressful life events," Nielsen said.

Researchers found a 71 percent increased risk of hospitalization from infectious disease for children who were exposed to their mother's stress while still in the womb.

Children whose mothers experienced a stressful event 11 months before conception had a 42 percent increased risk of hospitalization from infectious disease, but there was no association between a child's infectious disease risk and a mother's stress 12 to 35 months before conception (up to three years before conception), the study said.

And kids exposed to prenatal stress were 67 percent more likely to be hospitalized during their first year of life than kids whose mothers didn't undergo a major stressful event, according to the study.

Explaining the effects
The reasons why a mother's stress can carry over to her child's immune function aren't exactly known, but it's possible that a woman who experiences a stressful event while pregnant may also adopt unhealthy behaviors like smoking, drinking alcohol, eating poorly or using medications that could affect her child's immune system, Nielsen said.

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Biologically, it's also possible that maternal stress hormones, high amounts of which are produced during pregnancy, are transferred from mother to fetus, Nielsen said.

These stress hormones could be acting on a part of the fetal brain that regulates the immune system, said Kathleen M. Gustafson, director of fetal biomagnetometry at the University of Kansas Medical Center, who was not involved with the study.

Poor immune function is not the only aspect of health that can be affected by maternal stress, Gustafson said. Preterm birth, being born small for gestational age, spontaneous abortions, developmental delays and increased risk of schizophrenia are all possible effects, she said.

"Normal pregnancy, in and of itself, is a maternal metabolic stress test," Gustafson told MyHealthNewsDaily.
Past research has also shown that mothers who are stressed out during pregnancy have kids with heightened immune systems and an increased sensitivity to allergens.

Harvard Medical School researchers presented work in 2008 to the American Thoracic Society that showed that the higher the level of prenatal stress mothers were exposed to, the higher the expression of immunoglobulin E in their babies' cord blood. Immunoglobulin E is a marker of a person's immune system — the more there is, the higher the risk of asthma and allergy.

However, it's important to note that the stressful events in the new study are different from the normal kinds of stress people encounter every day, Gustafson said.

"This publication deals with significant, life-altering events; not the kind of daily events we call 'stress' like getting stuck in traffic or missing your flight at the airport," Gustafson said. "We need to 'stress' that, if you will — otherwise we're causing undue stress to women who are doing their best to maintain a healthy pregnancy."

Pass it on: The kids of women who were stressed out from a major life-altering event while pregnant or a year before conception are at an increased risk of being hospitalized from infectious disease.

Follow MyHealthNewsDaily staff writer Amanda Chan on Twitter @ AmandaLChan.

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