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3/9/2006 12:07:00 AM

Rice sociologist finds premature birth increases risk for asthma

BY PAM SHERIDAN
Special to the Rice News

In the past two decades, asthma has become the No. 1 chronic disease among children in the U.S. under age 18, most notably within this country’s impoverished populations. In a new study of Puerto Rican children, who have the highest asthma rates among racial and ethnic groups in the U.S., researchers at Rice University determined that the risk factors associated with the disease vary depending on whether a child is born prematurely or as a full-term infant.

Bridget Gorman

“For example, socioeconomic status and environmental factors, such as poverty and living in an unclean home, increase the risk of asthma among term children, but are not related to asthma among preterm children,” said Bridget Gorman, assistant professor of sociology.

Factors critical to preterm children are the need for assisted ventilation immediately after birth and their mothers’ health behavior — whether the mother smoked during her pregnancy and breast-fed her child. However, while breast-feeding can significantly lower the odds of a child developing asthma, the effect is strongest among the youngest preterm children. As the gestational age of the child at birth increases, the protective effect of breast-feeding is diminished, Gorman said.

While the researchers found that asthma rates among Puerto Rican children are associated with their socioeconomic status, the connection is stronger for full-term infants. The asthma rate for full-term infants living in deep poverty, for example, is twice as high as the rate for non-poor children, while premature infants in deep poverty have 1.4 times the asthma rate as non-poor children. The researchers also determined that asthma rates for both term and preterm children are higher in families with incomes just above the poverty line (100 to 150 percent), when compared with children living just below the poverty line.

“The relationship we show between poverty and asthma underscores the critical need not only to help those who are desperately poor, but those who hover close to the poverty line where they may be ineligible for all sorts of needs-based social services,” Gorman said.

In the study, published in Population Research and Policy Review, sociologist Nancy Landale with Pennsylvania State University’s Population Research Institute joined Gorman to examine the role of socioeconomic and environmental conditions and maternal health behavior in the development of asthma among young Puerto Rican children.

Gorman and Landale relied on data from the Puerto Rican Maternal and Infant Health Study, which included an analytic sample of 1,173 Puerto Rican children drawn from 1994-1995 computerized birth certificates in states where more than 72 percent of all births to Puerto Rican women occurred. Mothers of the sampled infants were asked to participate in a computer-assisted personal interview.

In addition to establishing whether a child was born premature, the researchers measured the family’s socioeconomic status, its indoor and outdoor environment and the mother’s health behavior.

Gorman and Landale found that the association between some socioeconomic and environmental factors and asthma differs between full-term and preterm children. Asthma rates, for example, are more than twice as high for children whose mothers did not finish high school, compared with children whose mothers had college degrees. However, the researchers noted that the association between maternal education and asthma differs for preterm and full-term children.

“Asthma rates for preterm children are significantly higher when the mother has a high school diploma than when she did not complete high school,” Gorman said. “For term infants, however, asthma rates were shown to be much lower among children of high school graduates versus those whose mothers didn’t graduate.”

While this finding appears counterintuitive, Gorman said the growing portion of premature births across the U.S. population over the last several years could be attributed to mothers who are using fertility treatments.

“Mothers who can afford fertility drugs are more likely to be better off economically and have better educations,” Gorman said. “In general, preterm infants in our sample were significantly less likely to be impoverished and were born to more highly educated mothers than their term counterparts.”

While living in an unclean home significantly increased the odds of asthma, the children’s outdoor environments did not appear to play a role in developing asthma.

In looking at the children’s demographics, the researchers found a number of variables related to the odds of childhood asthma. Girls, for example, are less likely than boys to develop the disease. Odds are lower for children with relatively old mothers and more than twice as high for those who have older siblings versus those with no older brothers or sisters.

“Our study not only confirms a strong connection between [premature birth] and childhood asthma, it also shows that the social and environmental factors that put children at risk for this disease are the same factors that harm the health of children in general,” Gorman said.