Tobacco smoke exposure has been associated with early childhood asthma symptoms. We assessed the associations of tobacco smoke exposure during pregnancy and childhood with wheezing patterns, asthma, airway interrupter resistance (Rint), and fractional exhaled nitric oxide (Feno) in school-age children and whether birth characteristics explained the associations.
This study was embedded in a population-based prospective cohort study among 6,007 children. Paternal and maternal smoking during pregnancy (never, first trimester only, continued), secondhand tobacco smoke exposure during childhood, wheezing patterns, and asthma were prospectively assessed by questionnaires. Wheezing patterns were defined as never, early (≤ 3 years only), late (> 3 years only), and persistent (≤ 3 and > 3 years) wheezing. Rint and Feno were measured at age 6 years. Birth characteristics were available from registries.
Continued maternal smoking during pregnancy was associated with increased risks of early and persistent wheezing (OR: 1.24 [1.01, 1.52]; 1.48 [1.13, 1.95]) and asthma (1.65 [1.07, 2.55], for at least five cigarettes per day), but not with Rint or Feno. Birth characteristics did not explain these associations. Childhood tobacco smoke exposure was associated with higher Rint (difference z score: 0.45 [0.00, 0.90]), but this effect attenuated after adjustment for birth characteristics. Maternal smoking during first trimester only or paternal smoking during pregnancy was not associated with Rint, Feno, wheezing, or asthma.
Continued maternal smoking during pregnancy was associated with increased risks of asthma outcomes in school-age children, whereas childhood tobacco smoke exposure was associated with higher Rint. Birth characteristics may explain part of these associations.