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Newborns of mothers who smoke during pregnancy show lower levels of stress hormones, lowered stress response, and alterations in DNA for a gene that regulates passage of stress hormones from mother to fetus, according to a new study. 

"Our results suggest that these newborns may not be mounting adequate hormonal response to daily stressors. Their stress systems may not be prepared for the stressors of daily life," said lead researcher Laura Stroud, Ph.D., of the Centers for Behavioral and Preventive Medicine at The Miriam Hospital, in the press release. "This may be particularly detrimental in babies born to mothers who lack resources and parenting skills and whose babies may encounter more daily stressors."

According to statistics, approximately one in 10 expectant moms in United States continue to smoke during pregnancy. The rates are higher among young. poor, and undeserved moms. 

Babies born to smoking mothers are born smaller, are more likely to be premature, and are at greater risk for medical complications, the press release added. 

"One possibility is alterations in stress hormones and epigenetic changes (chemical modifications) in DNA" Stroud said. "We were interested in stress hormones because alterations in stress hormones have been linked to both smoking and behavior problems and because maternal stress hormones during pregnancy exert potent long-term effects on offspring. In particular, we sought to investigate effects of smoking during pregnancy on the newborn stress hormone cortisol." Cortisol is part of the hypothalamic pituitary adrenocortical system that works synergistically with the "fight flight" stress system.

The study is published in the journal Psychoneuroendocrinology.