EFFECTS OF SMOKING CESSATION ON MATERNAL AIRWAY FUNCTION AND BIRTH-WEIGHT

Objective: To evaluate the effects of smoking cessation before or earl y in pregnancy on maternal airway function and birth weight. Methods: Measurements of forced expiratory spirometry including forced vital ca pacity, forced expiratory volume in I second, forced expiratory now ra tes between 0.2 and 1.2 L, 25% and 75%, and 75% and 85%, and instantan eous hows at lung volumes of 25%, 50%, and 75% were carried out by a w edge bellow spirometer in 40 pregnant exsmokers and were compared with those of 175 nonsmoking and 97 currently smoking pregnant women. Spir ometric testing was conducted at a mean (+/- SD) gestational age of 21 .5 +/- 7.0 weeks. In exsmokers, the average lifetime cigarette consump tion was 17.1 +/- 8.1/day for a mean duration of 9.7 +/- 3.9 years, si milar to that observed in current smokers. The median duration of smok ing abstinence was 20 weeks before study spirometry. Results: All spir ometric measurements in exsmokers were similar to those of nonsmokers and were significantly higher than those of current smokers. Spirometr ic measurements for nonsmokers, current smokers, and exsmokers were re spectively: forced expiratory volume in 1 second (3.36 +/- 0.39, 3.09 +/- 0.45, and 3.35 +/- 0.32 L); forced expiratory now rate between 25% and 75% (ie, mid-expiratory phase) (3.85 +/- 0.69, 3.21 +/- 0.76, and 3.86 +/- 0.66 L/sec); forced expiratory flow rate between 75% and 85% (ie end-expiratory phase) (1.39 +/- 0.35, 1.03 +/- 0.35, and 1.41 +/- 0.39 L/sec); instantaneous now at lung volume of 50% (4.35 +/- 0.82, 3.76 +/- 0.89 and 4.360.68 L/sec); and instantaneous now at lung volum e of 25% (1.91 +/- 0.47, 1.47 +/- 0.49, and 1.92 +/- 0.46 L/sec). Mean gestational age at delivery was similar among the three groups (277 /- 11, 274 +/- 12, and 274 +/- 11 days for nonsmokers, current smokers , and exsmokers, respectively). The mean birth weight of babies born t o exsmokers (3408 +/- 511 g) was similar to that of babies born to non smokers (3469 +/- 461 g), but was significantly greater than that of b abies born to smoking pregnant women (3189 +/- 485 g; P < .001). Concl usions: Smoking cessation either before or at an early stage of pregna ncy is associated with early, reversible increments of maternal airway function and mean birth weights that are higher than among women who continue smoking. (Obstet Gynecol 1998;92:201-5. (C) 1998 by The Ameri can College of Obstetricians and Gynecologists.)