Fetal growth and length of gestation in relation to prenatal exposure to environmental tobacco smoke assessed by hair nicotine concentration.

We assessed the effects of prenatal exposure to environmental tobacco smoke on fetal growth and length of gestation. The study population consisted of 389 nonsmoking women who were selected from a population-based study in southeast Finland on the basis of questionnaire information after delivery (response rate 94%). The final exposure assessment was based on nicotine concentration of maternal hair sampled after the delivery, which measures exposure during the past 2 months (i.e., the third trimester). The exposure categories were defined a priori as high (nicotine concentration [Greater and equal to] 4.00 microg/g; n = 52), medium (0.75 to < 4.00 microg/g; n = 186), and low as the reference category (< 0.75 microg/g; n = 151). In logistic regression analysis, controlling for confounding, the risk of preterm delivery (< 37 weeks) was higher in the high [adjusted odds ratio (OR) = 6.12; 95% confidence interval (CI), 1.31-28.7] and medium exposure categories (adjusted OR = 1.30; 95% CI, 0.30-5.58) compared with the reference category, and there was a 1.22 (95% CI, 1.07-1.39) increase in adjusted OR with a 1 microg/g increase in hair nicotine concentration. The corresponding adjusted OR was 1.06 (95% CI, 0.96-1.17) for low birth weight and 1.04 (95% CI, 0.92-1.19) for small-for-gestational-age.