BACKGROUND Exposure to environmental tobacco smoke (ETS) during childhood and in utero exposure to maternal smoking are associated with adverse effects on lung growth and development.

RESULTS In utero exposure to maternal smoking was associated with reduced peak expiratory flow rate (PEFR) (–3.0%, 95% CI –4.4 to –1.4), mean mid expiratory flow (MMEF) (–4.6%, 95% CI –7.0 to –2.3), and forced expiratory flow (FEF₇₅) (–6.2%, 95% CI –9.1 to –3.1), but not forced expiratory volume in one second (FEV₁). Adjusting for household ETS exposure did not substantially change these estimates. The reductions in flows associated with in utero exposure did not significantly vary with sex, race, grade, income, parental education, or personal smoking. Exposure to two or more current household smokers was associated with reduced MMEF (–4.1%, 95% CI –7.6 to –0.4) and FEF₇₅ (–4.4%, 95% CI –9.0 to 0.4). Current or past maternal smoking was associated with reductions in PEFR and MMEF; however, after adjustment for in utero exposure, deficits in MMEF and FEF₇₅ associated with all measurements of ETS were substantially reduced and were not statistically significant.

CONCLUSIONS In utero exposure to maternal smoking is independently associated with decreased lung function in children of school age, especially for small airway flows.