Women who smoke during pregnancy may be twice as likely to give birth to a child with behavioral problems like attention deficit hyperactivity disorder (ADHD).

A new study shows that smoking during pregnancy doubled the risk of having a child with ADHD or other behavioral disorders that involve hyperactivity, inattention, and acting impulsively, known as hyperkinetic disorders.

Experts have long recommended that women stop smoking during pregnancy in order to reduce the risk of birth defects and other problems. But this study suggests that exposure to nicotine in the womb may also affect the development of the baby's brain and increase the risk of behavioral problems like ADHD.

Researchers say ADHD and hyperkinetic disorders are the most common psychological problems diagnosed in children. The two behavioral problems include many of the same symptoms and were treated as one in the study.

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Another Reason to Quit During Pregnancy

In the study, Danish researchers examined the association between smoking during pregnancy and ADHD in 170 children with the behavioral problem and more than 3,700 healthy children matched by age, sex, and date of birth.

Initially researchers found women who smoked during pregnancy were three times as likely to have a child with ADHD as nonsmokers.

But researchers say the effect of nicotine exposure in the womb is only one of many factors, including environment, socioeconomic status, and a family history of mental disorder, that may affect a child's likelihood of developing behavioral problems.

After taking these risk factors into account the researchers found the effect of smoking during pregnancy doubled the risk of having a child with ADHD.

The results of the study appear in the August issue of Pediatrics.

Read WebMD's "10 Little-Known Reasons to Quit Smoking"

By Jennifer Warner, reviewed by Brunilda Nazario, MD

SOURCE: Linnet, K. Pediatrics, August 2005; vol 116: pp 462-467.