Postnatal growth and childhood asthma in preterm and full-term twins: A cohort study.

BACKGROUND: The role of postnatal growth in asthma development in children remains unclear. We examined the association between postnatal growth pattern and childhood asthma and assessed whether this association differed between preterm and full-term children. METHODS: This cohort study included twins from the Child and Adolescent Twin Study in Sweden (born 1992-2003), linked to national registers. Postnatal weight and height to age 5 were obtained from child health records and standardized for age and sex (SDS). Childhood asthma was defined by parent-reported asthma at age 9 or 12. Analyses were stratified by preterm (<37 weeks) and full-term birth. RESULTS: Among 3059 children, 15.6% developed asthma, 38.3% were born preterm. On average, the asthma group had 0.16 lower weight and 0.27 lower height SDS during the first 6 months, with no growth differences between asthma and non-asthma groups thereafter. These early differences were apparent among preterm children. From the identified growth trajectories, normal birth size with subsequent normal growth occurred in 79.1% of full-term and 41.9% of preterm children. A group with low birth size followed by catch-up growth was associated with an increased odds of asthma (adjusted OR: 1.68, 95% CI: 1.16-2.45). CONCLUSIONS: Postnatal growth differences between children with and without asthma were limited to the first months of life among those born preterm, with similar growth patterns thereafter up to age 5 and among full-term children. Among the identified growth trajectories, childhood asthma was most prevalent in those with low birth size and subsequent catch-up growth.