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12/15/2005

Premature birth rates increases asthmas risk, study finds

The association between poverty and asthma, the number one chronic disease among U.S. children, is well established.  However, a new study by university researchers shows a strong connection between premature birth and childhood asthma, as well as some surprising results -- for example, asthma rates for preterm infants were higher when the mother was a high school graduates than when she was not.

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In the past two decades, asthma has become the number one chronic disease among children in the U.S. under age 18, most notably within this country's most impoverished populations. In a new study of Puerto Rican children, who have the highest asthma rates of any racial or ethnic group in the U.S. , researchers determined that the risk factors associated with the disease vary depending on whether a child is born prematurely or as full term infants.

"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," says Rice University sociologist Bridget Gorman.

More critical to preterm children, according to Gorman, is the need for assisted ventilation immediately after birth and their mothers' health behavior -- whether the mother smoked during her pregnancy and if she 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.

While the researchers found that asthma rates among Puerto Rican children are associated with their socioeconomic status, the connection is stronger for term infants. The asthma rate for 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 - 150 percent above), when compared to 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 says.

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

In analyzing the effects of prematurity and social factors on childhood asthma among Puerto Ricans, Gorman and Landale relied on data from the Puerto Rican Maternal and Infant Health Study. The study's analytic sample of 1,173 Puerto Rican children was drawn from 1994-1995 computerized birth certificates in U.S. states where over 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 prematurely, the researchers measured the family's socioeconomic status, its indoor and outdoor environment and the mother's health behavior. They controlled for several demographic variables, namely, the mother's age, marital status, birthplace, the child's age and gender and whether there were any siblings.

Gorman and Landale report that the association between some socioeconomic and environmental factors and asthma differs between term and preterm children. Asthma rates, for example, are more than twice as high for children whose mothers did not finish high school compared to children whose mothers had college degrees. But, they note, the association between maternal education and asthma differs for preterm and 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 says.

"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 hypothesizes that the growing portion of premature births across the U.S. population over the last several years may be attributed to mothers who are using some type of fertility treatment.

"Mothers who can afford fertility drugs are more likely to be better off economically and have better educations," Gorman says.

"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, other factors that did not appear to play a role in young children developing asthma were their outdoor environment, after controlling for the family's socioeconomic status, their exposure to second-hand smoke after birth and the lack of medical insurance. 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 prematurity 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 concludes.

In addition to her research on racial and gender differences in morbidity and mortality, Gorman has studied the influence of early life social conditions on men's mortality as well as child and adolescent health and development. A member of Rice's sociology faculty since 2002, she received her undergraduate degree from Western Washington University and her master's and doctorate degrees in sociology and demography from Pennsylvania State University.

For more information on this research, please contact Gorman at bkgorman@rice.edu or Debra Thomas in the Jones School at dthomas@rice.edu .