Figure 3. Any Occurrence of Wheeze Between the Fourth and Sixth Birthday in Offspring of Pregnant Smokers Randomized to Vitamin C Supplementation (500 mg/d) vs Placebo During Pregnancy, Overall, and by Gestational Age at Randomization.

A, Multiple logistic regression was used to compare the occurrence of wheeze between offspring in the vitamin C and placebo treatment groups, adjusting for trial design factors of study site and gestational age at randomization and covariates of race and ethnicity and sex, and significant 2-way interactions of all of these variables. The analysis included 212 children (106 each in the vitamin C and placebo treatment groups). Children born to vitamin C–treated pregnant smokers had a significant decrease in current wheeze (28.3% vs 47.2%; estimated odds ratio, 0.41 [95% CI, 0.23-0.74]; P = .003). B, There was a significant interaction between treatment group and gestational age at randomization (P = .04), with children born to pregnant smokers randomized at 18 weeks of gestational age or earlier demonstrating the largest benefit from vitamin C treatment (odds ratio, 0.22 [95% CI, 0.09-0.54]). NS indicates not significant.

^aP = .001.