Smoking during pregnancy may cause later behavioral and emotional problems in children known as "conduct disorder."

The condition comprises an ongoing set of behaviors of significant social and clinical concern, researchers from the University of Leicester, England found in analyzing three previous studies. The findings draw from work showing an association between maternal smoking during pregnancy and conduct problems with children raised by either their mother or an unrelated maternal figure, such as an adoptive mother.

Such conduct problems may be a precursor to antisocial personality disorder in adulthood, and characteristic behaviors may include defiant or impulsive behavior, drug use, or criminal activity.

Darya Gaysina and her colleagues studied the link between maternal smoking during pregnancy — isolating the habit from post-natal smoking and other possible confounders — by analyzing a long-term study of mother-child pairs including biological and non-biological children, one that included only children adopted at birth, and one that followed children who'd been adopted at the time of conception by either genetically related or unrelated parents.

The average number of cigarettes each pregnant woman smoked per day was the measurement in the new analysis. The study found a strong link between smoking during pregnancy and later conduct problems among children birthed to those women, which did not change when raised by an adoptive parent.

"Our findings suggest an association between pregnancy smoking and child conduct problems that is unlikely to be fully explained by postnatal environmental factors — such as parenting practices — even when the postnatal passive genotype-environment correlation has been removed," the authors wrote Wednesday in the Journal of the American Medical Association, Psychology. "The causal explanation for the association between smoking in pregnancy and offspring conduct problems is not known but may include genetic factors and other prenatal environmental hazards, including smoking itself."

The study was praised by a scientist at Duke University Medical Center for isolating maternal smoking during pregnancy as the cause of the child's resultant behavioral problems. The researchers' "meta-analysis controls for perinatal and postnatal confounds including differences in child-rearing practices or the home environment," wrote Theodore A. Slotkin. "Thus, the conclusion is incontrovertible: prenatal tobacco smoke exposure contributes significantly to subsequent conduct disorder in offspring."

Science now knows the risks of maternal smoking during pregnancy persist long after birth, affecting a person throughout his or her lifespan.

"The impact of this article may provide a model for studying the effects of other toxicants so that the impact extends well beyond the implications of tobacco use in pregnancy," Slotkin said.

Source: Harold, Gordon T., Slotkin, Theodore A. Maternal Smoking During Pregnancy Associated With Offspring Conduct Problems. JAMA Psychiatry. 2013.