MedWire News: Children born to women who experience high levels of stress during pregnancy may be at greater risk of allergic diseases such as asthma than those born to women who experience relatively stress-free pregnancies, US study results suggest.

"While predisposition to asthma may be, in part, set at birth, the factors that may determine this are not strictly genetic," explained Dr Rosalind Wright, from Brigham and Women's Hospital and Harvard Medical School in Boston Massachusetts.

She added: "Certain substances in the environment that cause allergies, such as dust mites, can increase a child's chance of developing asthma and the effects may begin before birth."

Dr Wright and her team analysed stress levels and exposure to dust mite allergens among 387 pregnant women.

They then compared these findings with levels of an immune system antibody called immunoglobulin E - an indicator of sensitivity to allergens - in the women's children at birth.

The researchers found that children born to women who were highly stressed during pregnancy, even if they were exposed to low levels of dust mite allergens, had significantly higher levels of immunoglobulin E in their cord blood than those born to women who experienced low levels of stress.

The results remained true after accounting for the mother's race, education levels and smoking history, the team notes.

Speaking at the American Thoracic Society's International Conference in Toronto, Canada, Dr Wright said: "This research adds to a growing body of evidence that links maternal stress, such as that precipitated by financial problems or relationship issues, to changes in children's developing immune systems, even during pregnancy.

"This further supports the notion that stress can be thought of as a social pollutant that, when 'breathed' into the body, may influence the body's immune response similar to the effects of physical pollutants like allergens, thus adding to their effects."

She added that the children who participated in the study are now being monitored to see whether exposure to maternal stress in the womb is associated with an increased risk of asthma in later life.