Maternal smoking during pregnancy, environmental tobacco smoke exposure and childhood lung function

Background-Exposure to environmental tobacco smoke (ETS) during childhood a nd in utero exposure to maternal smoking are associated with adverse effect s on lung growth and development. Methods-A study was undertaken of the associations between maternal smoking during pregnancy, exposure to ETS, and pulmonary function in 3357 school c hildren residing in 12 Southern California communities. Current and past ex posure to household ETS and exposure to maternal smoking in utero were asse ssed by at self-administered questionnaire completed by parents of 4th,7th; and 10th grade students in 1993. Standard linear regression techniques wer e used to estimate the effects of in utero and ETS exposure on lung functio n, adjusting for age, sex, race, Hispanic ethnicity, height, weight, asthma , personal smoking, and selected household characteristics. Results-In utero exposure to maternal smoking was associated with reduced p eak expiratory flow rate (PEFR) (-3.0%, 95% CI -4.4 to -1.4), mean mid expi ratory 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 substantial ly change these estimates. The reductions in flows associated with in utero exposure did not significantly vary with sex, race, grade, income, parenta l 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 ass ociated 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 associat ed with decreased lung function in children of school age, especially for s mall airway flows.