Children whose mothers were exposed to second-hand smoke while pregnant may have a higher risk for psychiatric conditions such as attention deficit hyperactivity disorder than children of women without prenatal smoke exposure, according to an article published online May 13 by Child Psychiatry and Human Development.

In the first study to link second-hand (ambient) smoke exposure during pregnancy to psychiatric problems in children, psychologists Lisa Gatzke-Kopp and Theodore Beauchaine found evidence that the children of smoke-exposed mothers were at increased risk for attention deficit hyperactivity disorder (ADHD) and conduct disorder.

Symptoms that were more common in affected children included disorder symptoms, aggressive behavior, and defiance and conduct disorder.

The research also supports a 2006 report by the U.S. Surgeon General that found passive smoke exposure poses a substantial risk to the general health of those who breathe the smoke, as well as to the fetuses of pregnant women.

Gatzke-Kopp and Beauchaine compared patterns of psychopathology among three groups of 7- to 15-year-old children, all of whom had significant behavioral and/or emotional problems. One group had no prenatal smoke exposure. The second included children whose mothers smoked during the final two trimesters. The third consisted of children whose mothers were exposed to second-hand smoke at work or in the home during the last two trimesters. A total of 171 children, primarily boys, and 133 women participated in the project.

Children whose mothers had been exposed to smoke had more symptoms of attention deficit hyperactivity disorder and conduct disorder than children whose mothers spent their pregnancies in a smoke-free environment. However, they did not show more symptoms of emotional disorders such as depression or anxiety.

“This is a matter of severity,” said Gatzke-Kopp, a post-doctoral researcher.

“Children with these disorders have a range of behaviors that stretch from problematic to severe. It is a continuum based on the number of symptoms, and children who were exposed to smoke exhibited more symptoms.”

She and Beauchaine controlled for a number of other factors including family income, parents’ substance use, birth weight and parents’ anti-social behavior, but second-hand exposure to smoking persisted as the primary predictor of both disorders.

Nicotine is believed to cause these behavior problems in children. Animal studies have shown that nicotine affects brain development during the second and third trimesters of pregnancy, causing changes in brain regions critical to the development of externalizing psychopathology in humans.

“Evidence suggests that the dopamine system in the brain gets overstimulated during pregnancy,” Beauchaine said.” As a consequence, children who were exposed to smoke in utero have colic and are hard to soothe as infants. As toddlers they are overactive and oppositional. Later on they are irritable, inattentive and low on pleasure.”