BACKGROUND Impaired growth and development of the respiratory system during fetal and early postnatal life may have important implications for lung development and later lung health. The aim of this study was to examine the association of diminished premorbid airway function, prior wheezing, and maternal smoking with airway function at 1 year of age.

RESULTS At 1 year specific airway conductance during end expiration (sGawee; /s/kPa) was significantly diminished in those infants with prior wheezing (95% CI wheeze/no wheeze –0.76 to –0.14), mothers who smoked (95% CI smoke/no smoke –0.81 to –0.27), a family history of asthma (95% CI family history/no family history –0.62 to 0.00), or diminished premorbid sGawee (95% CI –0.13 to –0.43/s/kPa per unit reduction sGawee at 8 weeks). In a multivariate model only maternal smoking and diminished premorbid sGaweewere independently associated with diminished sGawee at 1 year.

CONCLUSIONS Diminished airway function at the end of the first year appears to be mediated by impaired airway development during early life as well as by exposure to maternal smoking. These findings are consistent with the hypothesis that, at a population level, diminished premorbid airway function provides the link between wheezing lower respiratory illness and diminished airway function at 1 year. Maternal smoking remains an important and avoidable cause of impaired airway development and function in infancy.