The researchers analyzed records from 177 boys, ages 7-12, who were referred to outpatient clinics for behavior problems. Among the 24 percent of mothers who reported smoking more than half-a-pack of cigarettes a day during pregnancy, 80 percent of their sons had conduct disorder. In comparison, conduct disorder was diagnosed in approximately 50 percent of the boys whose did not smoke.
"Our study indicates that regardless of other risk factors, smoking during pregnancy can have serious behavioral outcomes for children," said Lauren Wakschlag, Ph.D., assistant professor of psychiatry at the University of Chicago Medical Center and lead author of the study.
Approximately five percent of all children in the United States, ages 4-17, suffer from conduct disorder, which involves chronic, serious anti-social behavior problems. Symptoms include frequent and persistent lying, fire-setting, vandalism, physical cruelty, forcible sexual activity or stealing that begins much earlier than normal juvenile delinquency and is much more severe.
"Our study suggests that something as simple and preventable as maternal cigarette smoking could be a major cause of conduct disorder," said Ben Lahey, Ph.D., professor of psychiatry at the University of Chicago and co-author of the study.
"The implications of the study are tremendous," explains Lahey. "In one-third of cases, conduct disorder becomes adult antisocial personality disorder. These adults account for ten percent of all criminals but commit 50 percent of all crimes."
The overwhelming costs related to mental health, physical health, substance abuse, special education, and incarceration for children with conduct disorder, and adults with antisocial personality disorder, place a huge burden on their families and on society. Because treatment is rarely effective, the key is prevention.
The study authors suggest that maternal cigarette smoking is an important factor in conduct disorder because nicotine may disrupt fetal brain development. Research with animals suggests that nicotine directly affects the developing brain of the fetus, but there is not sufficient evidence to reach the same conclusion for humans. It is also possible that maternal smoking is not causally related to, but is a marker for some yet unknown risk factor for conduct disorder. The study controlled for some possible risk factors associated with conduct disorder such as socioeconomic status, parental psychopathology, maternal age at birth of the child, and family risk factors such as ineffective discipline. But, whatever the mechanism, maternal smoking during pregnancy is an important link to the development of conduct disorder.
Previous studies have linked cigarette smoking during pregnancy with low birthweight, prematurity, and infant mortality. Still, an estimated 20-25 percent of pregnant women smoke.
"Our study suggests that cigarette smoking may be one of the first prenatal risk factors for this very serious disorder," says Wakschlag. "The cost of intensive support to help pregnant women stop smoking is minuscule compared with the costs of treating conduct disorder."
Study researchers include Lauren S. Wakschlag, Ph.D., Benjamin B. Lahey, Ph.D., Bennett L. Leventhal, M.D., and colleagues at the University of Chicago and Rolf Loeber, Ph.D., and colleagues from the University of Pittsburgh.
More research is clearly warranted and is the focus of ongoing investigation at the University of Chicago Medical Center.