Preterm delivery and asthma risk: The results of a meta-analysis

This meta-analysis of 19 epidemiologic studies provides evidence that preterm birth is a risk factor for the development of asthma. The estimates of asthma risk varied considerably among the studies. For example, the risk of asthma developing was 7% to 36% higher in children who were born prematurely than in those born at term.

The analysis indicated that the mean age of the study population was a significant determinant of the heterogeneity among risk estimates. The association between preterm delivery and asthma was strongest in the younger age groups.

The authors discuss 3 possible explanations for the link between preterm delivery and asthma:

•Preterm delivery might increase the risk of asthma because the lungs of the premature infant are not fully developed anatomically or immunologically. As a result, the child is more susceptible to exposures that can cause asthma.

•Preterm delivery and asthma may have common genetic determinants. There is evidence that the duration of pregnancy is shorter in women with asthma.

•Some exposures that trigger asthma postnatally may also induce it prenatally. Exposure to cigarette smoke is one of the more obvious culprits.

The authors say that their findings suggest that physiologic airflow obstruction should be treated aggressively in preterm infants because it might signal the development of asthma. They also note the importance of preventive measures directed at the possible environmental causes of asthma.