Researchers at Columbia University in New York City have found new evidence that children whose mothers smoke during pregnancy are at much greater risk than other children for drug abuse and conduct disorder. The findings reinforce those of other studies spanning more than 25 years that have shown similar problems associated with prenatal exposure to smoke in children ranging from toddlers through teens. The study also revealed marked gender differences, with girls at significantly increased risk for drug abuse and boys at significantly increased risk for conduct disorder.
The investigators interviewed 147 mother-child pairs 3 times over 10 years, with the children ranging from ages 6 to 23 at the start of the study. Both mothers and children were interviewed on entry into the study, again 2 years after the initial interview, and, finally, about 10 years after the initial interview. Because the researchers followed the children through either adolescence or young adulthood-something few studies have done before-they were able to collect data about whether and when the children began to abuse drugs, says Dr. Myrna Weissman, the study's principal investigator.
Data were gathered on psychiatric and substance abuse disorders of parents; family environmental factors, such as divorce and family discord; and maternal factors, such as alcohol and coffee consumption and postnatal smoking, to rule out other explanations for the presence of drug abuse and conduct disorder.
The researchers found that maternal smoking during pregnancy has long-term effects on children's behavior and health that cannot be explained by any other factor included in the study. Risk for adolescent drug abuse in girls was more than 5-fold higher if their mothers smoked more than 10 cigarettes a day during pregnancy. Among boys whose mothers smoked more than 10 cigarettes a day, risk for the onset of conduct disorder was greater than 4-fold that of boys whose mothers did not smoke, with the increase appearing in boys younger than 13. The drug most frequently abused by both boys and girls was marijuana, and the most frequent combination of drugs abused was marijuana and cocaine. Of the females who abused drugs, 70 percent abused more than one.
Why boys exposed to smoking before birth should be at risk for conduct disorder and girls at risk for drug abuse remains to be understood, Dr. Weissman says. She speculates that the differences may be related to sex differences in prenatal brain development.
Many of the findings of this study are consistent with those of related studies, she notes. Researchers at the University of Chicago also have found a link between maternal smoking during pregnancy and conduct disorder in boys, she says. Likewise, a 1994 study conducted by Dr. Weissman's coinvestigator Dr. Denise Kandel found that maternal smoking during pregnancy increases risk for adolescent-onset smoking in girls. Studies also have found other behavioral problems in children exposed prenatally to smoke. For example, scientists at Massachusetts General Hospital found an association between prenatal exposure to smoke and attention deficit hyperactivity disorder. Similarly, a recent study by Dr. Judith Brook and her colleagues at Mount Sinai School of Medicine in New York City has found negative behavior in 2-year-olds of mothers who smoked during pregnancy.
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Wakschlag, L.S; Lahey, B.B.; Loeber, R.; Green, S.M.; Gordon, R.A.; and Leventhal, B.L. Maternal smoking during pregnancy and the risk of conduct disorder in boys. Archives of General Psychiatry 54:670-676, 1997.
Weissman, M.M.; Warner, V.; Wickramaratne, P.J.; and Kandel, D.B. Maternal smoking during pregnancy and psychopathology in offspring followed to adulthood. Journal of the American Academy of Child and Adolescent Psychiatry 38:7, 1999.