Does multiple gestation impact birthweight deficit from smoking?

Objective:to test the hypothesis that the combined birthweight deficit from smoking in twin gestation is significantly greater than previously described for singletons.study design:retrospective cohort study of white/black live-born twins, 32 to 40 weeks of gestation, 1990 to 2005, kansas city, mo. data were analyzed by t-test, χ2, linear and linear regression analyses.result:the cohort comprised 1190 twin pairs, 58% whites and 55% ⩾37 weeks. smoking rate was 14.5% and similar by race (14.2% white vs 14.8%, p=0.772). the aggregate birthweight of twins of nonsmokers was greater, 5116 g ± 25 g vs 4870 g ± 59 g, p<0.001 (mean±s.d.) and the difference was 264 g (95% confidence interval, 156 to 372 g) after adjusting for other variables in linear regression analyses.conclusion:smoking-associated growth restriction in twins is quantitatively similar to that of singletons. this finding is suggestive of dissipation or a ceiling effect to the growth-restricting effect of cigarette smoking.