Low birth weight not linked to childhood asthma

Jan 25 2013

By Mark Cowen, Senior medwireNews Reporter

Results from a US study do not support an association between low birth weight and an increased risk for childhood asthma.

In a study of 3933 children born between 1976 and 1979 in Rochester, Minnesota, the team found no significant difference between low (<2500 g) and normal birth weight (≥2500 g) infants in the cumulative incidence of asthma during the first 7 years of life, after propensity score matching to address covariate imbalance.

"While environment, genetics, and their interaction are thought to increase one's risk of developing asthma, we now should not assume that low birth weight is associated with asthma," said study author Hyeon Yang, from the Mayo Clinic in Rochester, in a press statement.

"This is an important finding as we continue to understand who is at risk for asthma and why," she added.

Overall, 6.7% of the 193 low birth weight children and 5.4% of the 3740 normal birth weight children developed asthma in the first 7 years of life.

However, there was significant covariate imbalance between the two birth weight groups regarding the number of prenatal visits, complications related to labor, induction of labor, maternal age at delivery, and marital status of parents.

To make the groups more comparable, the team used propensity scores, based on 16 covariates, to generate two matched groups of 109 low and normal birth weight children.

In these matched groups, nine (8.3%) of the low birth weight children and eight (7.3%) of the normal weight children developed asthma in the first 7 years of life - a nonsignificant difference.

Lead researcher Young Juhn, also from the Mayo Clinic in Rochester, and team conclude in the Annals of Allergy, Asthma and Immunology: "Our population-based study results indicate that low birth weight was not causally associated with risk of subsequent development of childhood asthma in the 1976 to 1979 Rochester birth cohort during the first 7 years of life."

They add: "We suggest that the propensity score approach may be a useful method to reduce covariate imbalance in observational studies concerning asthma epidemiology."

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