Does maternal smoking during pregnancy predict the smoking patterns of young adult offspring

Objective: To examine the association between maternal smoking during pregnancy and the development of smoking behaviour patterns among young adult offspring. Method: Data were from the Mater-University of Queensland Study of Pregnancy (MUSP), a birth cohort of 7223 mothers and children enrolled in Brisbane, Australia, in 1981. The development of smoking behaviours (early or late onset, or combination of onset and prevalence patterns) among offspring at age 21 years with different patterns of maternal smoking (never smoked, smoked before or after pregnancy but not during pregnancy, or smoked during pregnancy) were compared. Maternal smoking information was derived from the prospectively collected data from the beginning of pregnancy until the child was 14 years of age. Analyses were restricted to the 3058 mothers and children whose smoking status was reported. Results: The proportion of young adults who smoked regularly, either with early onset or late onset, was greater among those whose mothers had smoked during pregnancy compared with those whose mothers had never smoked. The smoking patterns among those adolescent offspring whose mothers stopped smoking during pregnancy, but who then smoked at other times during the child’s life, were similar to those whose mothers had never smoked. This association was robust to adjustment for a variety of potential covariates. Conclusions: The findings provide some evidence for a direct effect of maternal smoking in utero on the development of smoking behaviour patterns of offspring and provide yet another incentive to persuade pregnant women not to smoke. Abbreviations: FCV, first clinical visit; MUSP, Mater-University of Queensland Study of Pregnancy, SES, socioeconomic status In the natural history of smoking, there seems to be two critical periods for the development of nicotine dependence: in utero exposure and adolescence. Offspring of mothers who smoked during pregnancy experience many health and cognitive behavioural problems including asthma, respiratory infections, attention deficit and Tobacco Control 2006;15:452-457; doi:10.1136/tc.2006.016790 hyperactivity disorders, and difficulty with reading, mathematics and related skills. They are also more likely to smoke and become nicotine dependent. Most adolescent smokers continue to smoke as adults and those who start smoking early are more likely to continue smoking, to become daily smokers, to smoke heavily, to remain chronic heavy smokers and to become nicotine dependent. As the health effects of smoking are cumulative and substantial across the life course, identifying the origins of the development of smoking behaviours is of considerable public health importance. Nicotine passes through the placenta and may act directly on the developing fetal brain. Possibly, during a critical prenatal period of brain development, nicotine might modify the dopaminergic system implicated in the reinforcing effects of various classes of drugs including nicotine and change the response of this system to the effects of nicotine later in life. Prenatal exposure to nicotine is linked by both direct and indirect pathways to childhood hyperactivity, aggression and disruptive behaviour problems that increase the likelihood of smoking during adolescence. The indirect effects of nicotine on the fetus may also be secondary to poor maternal nutrition, exposure to carbon monoxide and restriction of blood flow to the placenta. With respect to the development of smoking behaviours, a few studies have found that in utero smoking predicts offspring smoking and nicotine dependence These studies suggest a positive association between maternal smoking during pregnancy and risk of smoking and nicotine dependence among offspring. To our knowledge, no studies have examined whether prospectively measured maternal smoking during pregnancy predicts different patterns of smoking in offspring (eg, occasional or more regular smoking), whether it predicts early or late onset, or whether it is influential in predicting a combination of onset and prevalence of smoking. With respect to reducing the public health burden of adolescent and young adult smoking, it is important to know whether in utero smoking is causally associated with these different patterns of smoking. One way to discern whether maternal smoking during pregnancy has a direct or indirect effect on patterns of offspring smoking is to compare the smoking patterns of offspring whose mothers smoked during pregnancy with those whose mothers smoked at times other than during pregnancy, and those who never smoked. If smoking during pregnancy directly affects later development of offspring smoking, then we would expect patterns of smoking among those whose mothers stopped smoking during pregnancy but smoked at other times during the child’s life to be more like those whose mothers never smoked. Alternatively, if the effects were indirect, via childhood hyperactivity, aggression and disruptive behaviour problems, then the effect of in utero smoking on offspring smoking would be mediated by these childhood factors. Consequently, if a mother gave up smoking during pregnancy but was otherwise a smoker, the smoking pattern of her offspring might differ from that of women who continued to smoke throughout pregnancy. A further possibility is that the effect results primarily through social modelling during adolescence, rather than being mediated by childhood behaviour problems. The aim of this study is to understand the mechanisms linking maternal smoking during pregnancy to the development of smoking behaviours among young adult offspring. The study involves different patterns of maternal smoking derived from Tobacco Control 2006;15:452-457; doi:10.1136/tc.2006.016790 prospectively collected data from the beginning of pregnancy until the child was 14 years of age.