Effect of cigarette smoking on maternal airway function during pregnancy.

The effects of cigarette smoking on maternal airway function during pregnancy were investigated in a cross-sectional study of 97 smokers and 175 nonsmokers at different gestational ages. The groups were comparable in age, height, and weight. All subjects were healthy. Forced vital capacity, forced expiratory volume in 1 second, their ratio, the forced expiratory flow rates between 0.2 and 1.2 L, 25% and 75%, and 75% and 85%, and instantaneous flows at lung volumes of 25%, 50%, and 75% were measured. All spirometric tests were unaffected by gestational age. However, all parameters of spirometry were significantly less in smokers than in nonsmokers when cumulative data during pregnancy were compared. Forced vital capacity, forced expiratory volume in 1 second, and their ratio were minimally reduced (4%, p less than 0.05; 8%, p less than 0.001; and 4%, p less than 0.001; respectively) in smokers as compared with nonsmokers. Larger reductions were noted in forced expiratory flow rates between 0.2 and 1.2 L (14%, p less than 0.001) and between 25% and 75% (16%, p less than 0.001), and in instantaneous maximum flows at lung volumes of 75% (11%, p less than 0.001) and 50% (13%, p less than 0.001). Maximum reduction of forced expiratory flow rates between 75% and 85% (26%, p less than 0.001) and in instantaneous flows at maximum lung volumes of 25% (23%, p less than 0.001) suggests marked increases in small-airway resistance and early small-airway disease in smokers. The progression of small-airway disease is related to the level of cigarette exposure. The results of our study demonstrate that the bronchodilatory effect expected in pregnancy is not sufficient to overcome the deleterious effects of cigarette smoking.