Women who take antibiotics during pregnancy are more likely to give birth to children with an allergy-related condition, such as asthma, hay fever or the skin condition eczema, according to a report published in the American Journal of Respiratory and Critical Care Medicine.

Doctors from the University of Nottingham in the U.K. reviewed medical records of 24,690 children and their mothers, and found that children who were exposed to antibiotics in the womb had a higher risk of developing these conditions than did children whose mothers did not take the medication during pregnancy.

The report noted that, "Approximately one third of the mothers were prescribed one or more courses of antibiotics during pregnancy and this exposure was associated with an increased incidence of all three allergic diseases."

Researchers couldn't say definitely what causes this link between antibiotic exposure and allergy conditions, but they suggested it might have to do with the fact that the immune system develops while the person is still in the womb. The exposure to infections and/or antibiotics may weaken the immune system and leave the child more vulnerable to allergic conditions.

"Our findings suggest that exposure to antibiotics and to infections in utero is a potentially important risk factor in the development of allergic disease," they concluded.

SOURCE: "The Importance of Prenatal Exposures on the Development of Allergic Disease: A Birth Cohort Study Using the West Midlands General Practice Database," by Tricia M. McKeever, Sarah A. Lewis, Chris Smith and Richard Hubbard. American Journal of Respiratory and Critical Care Medicine 2002;166:827-832.