March 22, 2011

Extreme Preterm Birth Linked To Higher Asthma Risk

Young adults who were born extremely premature may be at higher risk for asthma, according to a study published Monday in the journal Pediatrics.

The scientists followed more than 600,000 Swedish adults 25 to 35 years old to determine whether asthma medications were prescribed in 2005"“2007.   They found that those born between the 23rd and 27th weeks of pregnancy were 2.4 times as likely to have asthma as those born full-term.

However, no increased risk was seen among those born after the 27th week of pregnancy.

A full-term pregnancy lasts roughly 40 weeks, and any birth prior to week 37 is considered preterm.

The results were "somewhat unexpected," said Dr. Casey Crump, lead researcher of the study and an assistant professor of medicine at Stanford University.

Previous studies had suggested that respiratory problems after preterm birth typically wane during childhood, Dr. Crump told Reuters.

However, that research involved primarily young people who had been born moderately premature.

Until recently, very few extremely premature infants survived.  It is only now that there are enough such adults that large-scale studies can examine their long-term health profiles.

The current study is the first one to examine a large enough population to demonstrate a link between extreme prematurity and long-term asthma risk, the researchers said.

The results are based on data for all 622,616 singleton infants born in Sweden between 1973 and 1979.  In total, four percent were born prematurely, including 165 who were extremely preterm.  Of those born extremely premature, 9 percent had asthma drug prescriptions at some point between 2005 and 2007, compared with just 4 percent of both the full-term and moderately premature birth groups.

The researchers accounted for several other factors, such as socioeconomic status and maternal history of asthma, and found that young adults in the extremely premature group were 2.4 times more likely to have asthma than those in the full-term group.

Although the study does not prove that very early birth, itself, leads to asthma in some adults, Dr. Crump said the connection is possible.

"Preterm delivery can result in immature lung development, altered immune function that is needed for normal lung function, and increased susceptibility to infection or environmental factors such as smoking," he said.

Parents of highly-preterm children, and young adults who were born very premature, should be aware of the risk and have any respiratory problems checked by a doctor, he added.

It is "very important" that young people avoid smoking, which would further increase any increased asthma risk, he said.

It is unclear whether the increased asthma risk seen in this study group will necessarily remain true for infants born in recent years, Dr. Crump said.

"It's possible that their long-term risk may be different due to changes in neonatal care."

"It will take years to answer this question."

Some 7.3 percent of adults (16 million) and 9.4 percent of children (7 million) have asthma in the United States, according to the U.S. Centers for Disease Control and Prevention.  

The findings were reported online March 21 in the journal Pediatrics. 


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