In utero nicotine exposure and fetal growth inhibition among twins.

We examined the impact of cigarette smoking on fetal growth among twins by analyzing matched twin live births in the United States from 1995 through 1998. The outcomes of interest were low and very low birthweight, preterm and very preterm birth, and small for gestational age. Out of a total of 163,901 mothers, 19,234 reported active smoking during pregnancy (11.7%). Twins born to smokers weighed an average of 182 g less than their counterparts born to nonsmokers (p<0.001). The risk for fetal growth inhibition was greater among twins of smokers: low birthweight (adjusted odds ratio [OR], 1.84; 95% confidence Interval [CI], 1.79 to 1.89), very low birthweight (OR, 1.27; 95% CI, 1.21 to 1.32), preterm (OR, 1.3; 95% CI, 1.09 to 1.16), very preterm (OR, 1.18; 95% CI, 1.13 to 1.23), and small for gestational age (OR, 1.91; 95% CI, 1.84 to 1.98). In conclusion, prenatal smoking significantly inhibits fetal growth among twins, and small for gestational age appeared more affected than shortened gestation.