Intelligence in girls and their subsequent smoking behaviour as mothers: the 1958 National Child Development Study and the 1970 British Cohort Study.

BACKGROUND Exposure to tobacco smoke either in utero or postnatally can have substantial adverse effects on child health, yet many women continue to smoke during pregnancy and after the birth. How women's intelligence in childhood affects their smoking behaviour as mothers is unclear. METHODS The participants were from two British national birth cohorts: 3325 women aged 33 years from the 1958 National Child Development Study and 1971 women aged 34 years from the 1970 British Cohort Study. We used structural equation modelling to examine the direct and indirect effects of intelligence measured at age 10-11 years, parental and current social class, educational attainment and age at first birth on smoking during pregnancy and current smoking status. RESULTS Forty per cent of women in the 1958 cohort smoked during pregnancy, compared with 28% of those from the 1970 cohort. In both cohorts, women with lower IQ in childhood were more likely as adults to smoke during pregnancy and to be a smoker currently. Structural equation modelling showed that the effects of childhood IQ on smoking behaviour were indirect, as they were statistically mediated by educational attainment and age at first birth. There was some effect of educational attainment and age at first birth on smoking behaviour over and above the effect of intelligence. CONCLUSION Childhood intelligence influenced women's smoking behaviour as mothers primarily through its contributions to educational attainment and age at first birth.