Washington, Nov 4 Maternal smoking could increase the level of distress of newborns, according to a new study.

Previous studies have shown that prenatal cigarette smoke exposure is associated with increased rates of behaviour problems, irritability, attention-deficit/hyperactivity disorder, the risk of violent offenses, conduct disorder, adolescent onset of drug dependence, and the risk for criminal arrest in offspring.

The new study adds another potential negative outcome to the list of reasons for mothers to stop smoking while pregnant.

Most of the effects of tobacco either during pregnancy or on postnatal outcomes are attributed to nicotine.

However, smoking is associated with reduced monoamine oxidase A (MAO-A) activity, enzymes that degrade brain neurotransmitters in smokers.

Prenatal smoke exposure-induced low MAO-A activity in foetal life may dysregulate brain neurotransmission, creating a potential vulnerability to develop behavioural disorders later in life.

This dysregulation can occur with or without interaction with nicotine's effect on the developing brain.

French scientists compared blood biomarkers of MAO-A activity in smoking and non-smoking pregnant women and in the cord blood of their newborns.

They also assessed the newborns" comfort level during their first 48 hours of life and found that MAO-A activity is reduced both in pregnant smokers and in their newborns.

The newborns of smoking mothers also showed significantly more discomfort than those of non-smoking mothers, potentially related to MAO-A inhibition.

The study findings "may have implications for future research because it proposes a biological explanation for the previously demonstrated relationship between smoking during pregnancy and behavioural disorders in the offspring," said co-author Dr. Ivan Berlin.

The study is being published in the October 15th issue of Biological Psychiatry. (ANI)