Babies exposed to nicotine during pregnancy were more excitable and tense, the researchers say, and they showed signs of central nervous system and gastrointestinal stress.

The report, published in the June issue of Pediatrics, suggests the infants experienced "neonatal withdrawal" from nicotine, although the finding was not conclusive.

"Because we evaluated the babies at one to two days following birth, we don't know if it's actually withdrawal we're seeing or the effects of [the mother's] cigarette smoking," says study author Karen L. Law, a third-year medical student at Brown.

What's clear is that nicotine may have the same toxic effect as illegal drugs, Law adds. Ideally, the finding might motivate the 18 percent of pregnant women who smoke to quit.

The study compared the behaviors of 27 nicotine-exposed newborns and 29 unexposed newborns 48 hours after birth. The researchers measured the nicotine intake of mothers by asking them how many cigarettes they smoked per day and then verifying their answers by measuring a biological marker of nicotine called cotinine, which is found in saliva.

They found that a mother's cigarette intake correlated with an increase in symptom severity in her newborn.

"The present study is the first to establish that the predictions from animal models are indeed true -- behavioral abnormalities akin to those associated with illicit drugs used during pregnancy, are equally, or perhaps even more, detectable in the offspring of women who smoke during pregnancy," says Theodore Slotkin, a professor of pharmacology and cancer biology at Duke University Medical Center.

"This is an important, even essential, contribution to the field, especially as many of the women in the study were smoking fairly low numbers of cigarettes," he adds.

The results also suggest there may be legal grounds for removing children from mothers who smoke during pregnancy, say the researchers.

Given that nicotine is showing the same effects as an illegal substance for which protective services will remove babies from their mothers, policy makers ought to reconsider how they evaluate a fit mother, writes senior study author Barry Lester, a professor of psychiatry and human behavior at Brown.

"To have these results in which these nicotine-exposed babies have a similar profile as cocaine-addicted infants makes us take a step back and ask what's appropriate behavior during pregnancy. Somehow smoking is still acceptable," Law says. "We need to take a look at why one substance over another is not controlled during pregnancy."

The study did not look at the long-term impact of nicotine exposure during pregnancy, but the researchers say previous studies suggest the impact of smoking on newborns can be mediated if the family provides appropriate attention and care throughout childhood.

More information

For more on the dangers of smoking, see the U.S. Centers for Disease Control and Prevention, and here are the reasons why expectant moms should quit smoking.