Extensive evidence now supports a statistical association between prenatal
smoking and increased risk for antisocial outcomes in offspring. Though this
statistical link may signal a causal association, commentators have urged
caution in interpreting findings because of the likelihood of confounding.
We used data from the Environmental Risk Longitudinal Twin Study, a
representative British sample of 1116 twin pairs studied at ages 5 and 7 years,
to assess associations between prenatal smoking and early childhood conduct
problems net of the effects of both heritable and environmental risks for
child antisocial outcomes.
Prenatal smoking showed a strong, dose-response relationship with child
conduct problems at ages 5 and 7 years. Around half of this association was
attributable to correlated genetic effects. Mothers who smoked during pregnancy
differed from other mothers in a number of ways. They were more likely to
be antisocial, had children with more antisocial men, were bringing up their
children in more disadvantaged circumstances, and were more likely to have
had depression. Controlling for antisocial behavior in both parents, depression
in mothers, family disadvantage, and genetic influences, estimates for the
effects of prenatal smoking were reduced by between 75% and the entire initial
Observed associations between prenatal smoking and childhood conduct
problems are likely to be heavily confounded with other known risks for children's
behavioral development. As a result, tests of any causal influence of prenatal
smoking must await findings from experimental studies.