Figure 2. Airway Function Test Results Obtained by Spirometry Measurements at Age 5 Years in Children Born to Pregnant Smokers Randomized to Vitamin C Supplementation (500 mg/d) vs Placebo.

Spirometry measurements are shown for offspring of 93 and 99 pregnant smokers in the vitamin C and placebo treatment groups, respectively. P values were adjusted for trial stratification variables of study site and gestational age at randomization, sex, race and ethnicity, and height at testing. All forced expiratory flow (FEF) and forced expiratory volume in 1 second (FEV₁) measurements increased significantly in offspring of vitamin C–treated pregnant smokers. Of note, the ratio of FEF between 25% and 75% expired volume to forced vital capacity (FEF_25-75/FVC), an indicator of increased airway growth relative to lung volume (dysanapsis), was also significantly increased in the offspring of vitamin C–treated smokers. FEF₅₀ indicates FEF at 50% of expiration; FEF₇₅, FEF at 75% of expiration; and NS, not significant.

^aP < .01.

^bP < .05.