Prenatal exposure to tobacco and future nicotine dependence: population-based cohort study.

Background: Maternal smoking during pregnancy may increase the risk of nicotine dependence, especially in girls, but data are conflicting and confounding by other familial factors cannot be ruled out.

Aims: To clarify the relationship between prenatal tobacco exposure and adolescent tobacco uptake and dependence in boys and girls respectively, while taking confounding factors into close consideration.

Method: We conducted a prospective longitudinal study, comprising 3020 Swedish youths followed from 11 to 18 years of age. Exposure and outcome information was elicited via self-administered parental and repeated youth questionnaires. Hazard ratios (HRs), odds ratios (ORs) and corresponding 95% confidence intervals (CIs) were calculated as measures of associations.

Results: Girls prenatally exposed to maternal tobacco use had a two- to threefold increased odds of experiencing a high number of withdrawal symptoms (OR = 2.83, 95% CI 1.68-4.87), craving for tobacco (OR = 2.04, 95% CI 1.28-3.32) and heavy tobacco use (five or more cigarettes or snus dips per day) (OR = 1.93, 95% CI 1.30-2.86). These associations were weaker among boys, and did not reach formal statistical significance. Associations between prenatal tobacco exposure and onset of regular tobacco use in both genders appeared to be mostly explained by parents' social position and postnatal smoking behaviour.

Conclusions: Prenatal exposure to tobacco is linked to an increased risk of nicotine dependence among adolescent girls.