The effect of birth weight on lung spirometry in white, school-aged children and adolescents born at term: a longitudinal population based observational cohort study

Objective To evaluate how birth weight affects lung function measurements in childhood and adolescence in term-born children. Study design We used data for white, term-born, singletons, from the Avon Longitudinal Study of Parents and Children to determine the association between birth weight and lung function at age 8-9 (n = 4086) and 14-17 (n = 2582) years. z-scores for lung function measures, adjusted for sex, height, and age, were modeled in terms of birth weight z-score adjusted for sex. In addition, gestation and head circumference then confounders (maternal smoking during pregnancy and social class) were added to the model. Results At age 8-9 years, birth weight z-scores were significantly associated with lung function z-scores (forced expiratory volume in 1 second, forced vital capacity [FVC], and forced mid-expiratory flow between 25% and 75% of FVC). These relationships essentially were unchanged when birth weight z-scores were further adjusted for gestation, head circumference, and confounders, except for forced mid-expiratory flow between 25% and 75% of FVC, which was no longer significant after we adjusted for head circumference and confounders. At age 14-17 years, the associations between adjusted birth-weight z-scores and spirometry z-scores were in general not significant. Estimated differences for forced expiratory volume in 1 second were 30 mL at ages 8-9 years and 33 mL at 14-17 years for 1 kg change in birth-weight standardized for gestation and sex. Conclusions Birth weight is associated with lung function in term-born children at 8-9 years, but less so at 14-17 years, suggesting that birth weight influences lung function in early childhood but has lesser effect later in life