NEW YORK (Reuters Health) - Smoking during pregnancy has been linked to a higher chance of the child having attention-deficit/hyperactivity disorder (ADHD), and a new study suggests women who use nicotine replacement products may also have children with an elevated risk.
That doesn't necessarily mean that nicotine causes ADHD, the authors note.
For instance, it could be that women dependent on nicotine are more likely to have ADHD symptoms themselves, said senior author Dr. Carsten Obel, from Aarhus University in Denmark. The children of women who use nicotine replacement products to quit smoking may be at risk of ADHD because of genes or their family environment, he told Reuters Health by email.
For the new study, the researchers analyzed information from Danish databases on more than 80,000 children born between 1996 and 2002.
Mothers were interviewed while pregnant and asked if they currently smoked, used nicotine replacement products including gum, patches or sprays or had quit smoking before pregnancy without nicotine replacement. They also reported whether their husbands were current smokers.
The researchers then followed the children through 2011 and noted hospital diagnoses of ADHD or use of medication for the disorder. Roughly two percent of children in the study were diagnosed with ADHD.
Compared to children with nonsmoking parents, kids with two smoking parents were 83 percent more likely to develop ADHD, according to results published in Pediatrics.
Having a mother who smoked during pregnancy seemed to be a stronger predictor of ADHD risk than having a father who smoked.
Mothers who used nicotine replacement products had children with an increased risk of ADHD similar to the increase associated with smoking.
At this point, it is too soon to estimate how important nicotine exposure might be for ADHD risk, Obel said.
Mothers who had quit smoking and those who used nicotine replacement products both tended to have babies with higher, healthier birth weights than current smokers, he noted. Smoking during pregnancy is known to be associated with a lower birth weight for the baby.
"The nicotine patch doesn't decrease birth weight, which has been used as a target measure for a long, long time," said Yoko Nomura, who studies central nervous system development at The City University of New York's Queens College.
"We can't say the nicotine patch is useless because birth weight is so associated with many different illnesses," Nomura told Reuters Health. She was not part of the new study.
For most people, the risk of ADHD is very small to begin with, she said.
As of 2011, 11 percent of U.S. kids ages four to 17 had been diagnosed with ADHD, according to the Centers for Disease Control and Prevention.
Many factors can influence the risk of ADHD, and most of the important predictors are genetic, Nomura said.
"In order to prevent the non-genetic component of ADHD, we need to understand how smoking increases risk, and this doesn't help us learn more about that," she said.
Parents reporting their own smoking habits may not be very reliable, given the social pressure to quit during pregnancy, she noted.
"We have a long way to go before we can even conclude anything," Nomura said.
"The best advice will at this point probably be to try to stop smoking without use of nicotine replacement and preferably before getting pregnant," Obel said. "If this is not possible nicotine replacement is, based on the birth weight results, preferable in comparison with continuing to smoke."
For women who struggle to quit, even just cutting down on the number of cigarettes per day is a step in the right direction, Nomura said.