The Inter-Relationships of Extremely Low Birth Weight, Asthma, and Behavior: A Study of Common Cause, Mediation, and Moderation.

BACKGROUND

Extremely low birth weight (ELBW; <1000 g) infants are at risk for both asthma and problems like inattention, hyperactivity, anxiety, and depression. Asthma predicts behavioral and emotional problems in term-born children. The nature of these associations is poorly understood. We tested 3 models of association: independent risk, mediation, and effect modification to explore interplay among birth weight, asthma, and behavioral and emotional problems.

METHODS

We used data from a prospective cohort of ELBW infants born 1992 to 1995. Exposure was ELBW; primary outcomes were parent-reported diagnosis of asthma and symptoms of inattention, hyperactivity, anxiety, and depression at age 8 years. Covariates included child sex and maternal socioeconomic status.

RESULTS

There were 139 ELBW and 101 normal BW (>2500 g) children followed to 8 years. ELBW children were more likely to have asthma (35.7% vs 14.4%, P < .05). Inattention, hyperactivity, depression, and anxiety scores were higher among ELBW children and children with asthma. ELBW was a common cause of asthma and anxiety. There was no evidence of mediation or effect modification by asthma on the effect of ELBW on behavior and emotion symptoms.

CONCLUSION

Asthma does not underlie or amplify the effect of ELBW on behavioral and emotional problems at school age, suggesting that increased risk for respiratory morbidity and neurodevelopment represent largely independent consequences of developmental vulnerability related to ELBW. Noting the impact of chronic illnesses on neurodevelopment in other populations, data focused on symptom trajectories over time in a larger cohort may be necessary to shed further light onto this question.