That is the finding from an ongoing study by researchers at Harvard Medical School examining the impact of parental stress on child asthma risk in an inner city population.
Infants born to mothers who reported higher levels of stress during pregnancy showed increased sensitivity to allergen exposures, as measured by blood levels of an antibody that is a marker of immune response.
The association was seen even when prenatal exposure to a major environmental trigger of allergies and asthma was relatively low.
The findings, presented at the American Thoracic Society's 2008 International Conference in Toronto, suggest that maternal stress during pregnancy influences a child's developing immune system.
But most of the children in the study are still too young to have developed asthma, so it is too soon to say that prenatal exposure to stress plays a role in later asthma risk, researcher Rosalind J. Wright, MD, MPH, tells WebMD.
The oldest children in the study are now 4, and a few have not yet been born.
"We should know more in a few years, when most of these children are between the ages of 3 to 5," Wright says.
Poverty and Asthma
Almost one in 10 children in the U.S. has been diagnosed with asthma, and rates for African-American and Hispanic children are even higher, according to the CDC.
Living in poverty is recognized as an important risk factor for asthma, with the asthma rate almost twice as high for poorer kids as for those living in more economically advantaged families.
It was with this in mind that Wright and colleagues designed the Asthma Coalition on Community, Environment and Social Stress (ACCESS) project, one of the most rigorous studies ever to explore the potential causes of asthma in a minority and urban population.
"While predisposition to asthma may be, in part, set at birth, the factors that may determine this are not strictly genetic," Write notes. "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."
The newly reported findings included data on 387 infants born to study participants closely followed during pregnancy.
Researchers analyzed levels of maternal stress during pregnancy through questionnaires; exposure to dust mite allergen was measured during home visits.
Immune response at birth was measured by analyzing blood levels of the antibody immunoglobulin E (IgE) in the umbilical cord.
More Stress = Higher IgE
The researchers found increased levels of IgE expression in cord blood from infants whose mothers experienced higher levels of stress, even when exposed to relatively low levels of dust mite allergen during pregnancy.
The most frequently reported stress events were related to finances, health, relationships, and concerns about community safety.
Babies born to women who experienced three major stress events during pregnancy had a 12% increase in risk of giving birth to a child with an altered immune response, as measured by IgE, researcher Jeanette Peters, PhD, tells WebMD.
The highest IgE levels were seen in babies born to mothers who experienced the most stress and had the most dust mite exposure during pregnancy.
The children will continue to be followed until they reach age 5 or 6 to better understand the role of pregnancy stress and other environmental influences in the development of asthma.
But there is already a public health message from the research, Peters says.
"We have to have a multi-pronged approach to intervention," she says. "If we just reduce allergen levels and the mothers are still experiencing high stress there could still be an immune effect on the child at birth."