Smoking While Pregnant May Fuel Behavior Problems in Kids

Megan Brooks

July 24, 2013

Smoking during pregnancy is an independent prenatal risk factor for conduct problems in children, according to results of a new study.

The analysis is unique because it used "3 complementary genetically sensitive research designs" to examine the association between maternal smoking during pregnancy and child conduct problems, in which children were reared by genetically related and genetically unrelated mothers, Gordon T. Harold, PhD, of University of Leicester, United Kingdom, told Medscape Medical News.

"Using this approach, we were able to uniquely examine the role of genetic and prenatal risk factors (eg, smoking in pregnancy) relative to well-established postnatal risks, such as harsh parenting practices, in accounting for the development of children's conduct problems," he explained.

The study was published online July 24 in JAMA Psychiatry.

Dose-Response Pattern

Data for the analysis came from the Christchurch Health and Development Study (CHDS) in New Zealand, the Early Growth and Development Study (EGDS) in the United States, and the Cardiff IVF (C-IVF) Study in the United Kingdom.

The CHDS provided data on 1088 children reared by genetically related mothers and 36 children reared by genetically unrelated adoptive mothers; the EGDS provided data on 310 children reared by genetically unrelated adoptive mothers; and the C-IVF Study contributed data on 636 children reared by genetically related mothers and 206 children reared by genetically unrelated mothers.

The main outcome was conduct problems between ages 4 and 10 years reported by parents or teachers using standard instruments.

Across all 3 studies, children of mothers who smoked during pregnancy had more conduct problems than children of mothers who did not smoke during pregnancy. This was true for children reared by biological or adoptive mothers.

And there appeared to be a dose-response relationship; children whose mothers smoked 10 or more cigarettes per day had the highest average scores of conduct problems.

In a fully adjusted model, the link between maternal smoking during pregnancy and child conduct problems was statistically significant in the genetically related mother-child pairs in the CHDS (P = .03) and the C-IVF Study (P = .04). In the genetically unrelated mother-child pairs, the association was statistically significant in the EGDS (P = .01) but was attenuated in the CHDS (P = .12). This pattern of findings was also seen in a meta-analysis across pooled study samples.

Dr. Gordon Harold

Dr. Harold and colleagues say their findings point to an association between smoking during pregnancy and child conduct problems that is "unlikely to be fully explained by postnatal environmental factors (ie, parenting practices) even when the postnatal passive genotype-environment correlation has been removed."

"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," they add.

"These results," Dr. Harold told Medscape Medical News, "highlight the importance of considering factors that influence children both prior to birth as well as following birth in understanding the developmental origins of conduct problems — a set of problems recognized as affecting a rising proportion of youth (boys and girls aged 5 to 15 years) both nationally and internationally."

"Incontrovertible" Evidence

The author of a linked editorial says the study provides evidence that is "incontrovertible: prenatal tobacco smoke exposure contributes significantly to subsequent conduct disorder in the offspring."

"Considering the relationship of conduct problems to poor school performance, social isolation, and juvenile and adult incarceration, the negative impact on the affected individuals' quality of life and, ultimately, on society as whole, cannot be underestimated," writes Theodore A. Slotkin, PhD, of Duke University Medical Center in Durham, North Carolina.

"We can now recognize that maternal smoking during pregnancy creates a population of individuals at greater risk for specific behavioral disorders and we can be better prepared to recognize and ameliorate the consequences," Dr. Slotkin says.

More broadly, Dr. Slotkin thinks the approach taken by the researchers may be useful in resolving similar issues for other tobacco-related neurobehavioral disorders, such as attention-deficit/hyperactivity disorder (ADHD) and cognitive and emotional disorders, and potentially for prenatal exposures to other suspected neurobehavioral teratogens.

"The past 2 decades have seen an explosive increase in the incidence of neurodevelopmental disorders that likely involve exposure to neurotoxic chemicals in the environment. Thus, 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," Dr. Slotkin concludes.

The authors have disclosed no relevant financial relationships. Dr. Slotkin has received consultant income in the past 3 years from the following firms: the Calwell Practice (Charleston, West Virginia); Finnegan, Henderson, Farabow, Garrett, and Dunner (Washington, DC); Carter Law (Peoria, Illinois); Gutglass, Erickson, Bonville, and Larson (Madison, Wisconsin); the Killino Firm (Philadelphia, Pennsylvania); Alexander Hawes (San Jose, California); Pardieck Law (Seymour, Indiana); Tummel and Casso (Edinburg, Texas); Shanahan Law Group (Raleigh, North Carolina); and Chaperone Therapeutics (Research Triangle Park, North Carolina).

JAMA Psychiatry. Published online July 24, 2013. Abstract, Editorial

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