TORONTO — Mothers who smoke during pregnancy are not only increasing the risk of their babies being born with a low birth weight, respiratory problems and getting sudden infant death syndrome, but their children are also more likely to become obese as teenagers, according to a Canadian study.

The research, published Tuesday in the journal Obesity, is the first to draw a link between pre-natal cigarette exposure and teenage abdominal obesity.

The joint study from the University of Montreal and McGill University looked at 500 people between the ages of 12 and 18. Half the group had mothers who had smoked up to 11 cigarettes a day throughout their pregnancies. The other half was not exposed to cigarette smoke in the womb.

There were no significant weight differences among the younger teenagers of either group.

The older teenagers who were born to smoking mothers, however, had 26 per cent more body fat and 33 per cent more fat in their abdomens than teenagers whose mothers didn't smoke.

The study also found that those who were exposed to cigarette smoke also weighed 300 grams less at birth and breastfed a shorter period of time than their peers.

One of the lead researchers said although a causal link could not be established in this study between smoking and birth weight or breastfeeding time, other studies involving animals have indicated that nicotine may have an impact on brain functions that control eating impulses and energy metabolism.

"We believe that maternal cigarette smoking during pregnancy plays an important role in the fetal programming of obesity," Dr. Zdenka Pausova, a scientist at the Hospital for Sick Children, said in a statement. "Although we do not know the exact mechanisms, we know that nicotine in cigarette smoke, for example, sets into the baby's body and stays there in higher quantities and for longer than in the mother's."

Pausova said this should be another deterrent for mothers not to smoke while pregnant, because obesity in teenagers may lead to a number of illnesses including diabetes, hypertension and cardiovascular disease.