NEW YORK (Reuters Health) - Infants whose mothers smoke both during and after pregnancy have an increased risk of suffering chronic ear infections, researchers report.

"There's plenty of problems that infants exposed to smoke in the womb have--ear infections are another possible propensity," study author Dr. Judith E. C. Lieu, an instructor in the department of otolaryngology at Washington University School of Medicine in St. Louis, Missouri, told Reuters Health. "It's one more reason to get mothers to quit smoking (while pregnant)."

Previous research has shown that children whose parents smoke are at greater risk of developing ear infections. However, because having a mother who smokes seems to be a risk factor, the researchers were unclear whether the greatest risk occurs from smoke encountered during pregnancy or after birth.

"People have not been paying as much attention to in utero exposure," Lieu said. However, three out of four women smokers continue smoking while they are pregnant, Lieu noted. Some studies suggest that a mother who smokes may affect the immune system of her infant, possibly leaving the child more susceptible to later ear infections.

Lieu and colleagues analyzed data from a national health survey of more than 11,000 children under the age of 12. The survey included data on how often the children developed ear infections, whether they were exposed to secondhand cigarette smoke, and whether their mothers smoked during pregnancy.

The researchers also looked at factors that have been found to increase the risk of developing ear infections, including child care outside the home and a lack of breastfeeding.

Overall, 38% of the children were exposed to secondhand smoke, with 23% exposed to any smoke in the womb and 19% exposed to smoke both in the home environment and during gestation, according to the report in the February issue of the Archives of Pediatric and Adolescent Medicine.

The researchers found that the risk of ever suffering an ear infection was not increased by post-natal exposure to smoke, but was slightly increased by being exposed to smoke in the womb or by being exposed to smoke both before and after birth. In addition, the risk of suffering chronic ear infections, defined as more than 6 episodes in a lifetime, was 44% higher when children were exposed to smoke both during pregnancy as well as after birth.

"Exposure to smoke in utero seems to have an effect that works in combination with smoke exposure in the home," Lieu said. However, the study does not make clear whether smoking during gestation alone is the main risk factor for later ear infections, or whether it is the combination of the two exposures, she said.

"I don't think I have definitive answers," she said. "It really raises more questions."

SOURCE: Archives of Pediatric and Adolescent Medicine 2002;156:147-154.

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