Many women who quit smoking when they get pregnant start again after they give birth, often because they are worried about their weight, WebMD reported Sept. 15.

Researchers found that among women who quit smoking while pregnant, those who did not think of smoking as a weight-control tool were the most likely to remain abstinent after their children were born. On the other hand, those who were worried about controlling their weight were less motivated to stay off cigarettes after delivery.

"Two-thirds of women who quite smoking when pregnant will resume smoking after giving birth," said researcher Michele Levine, Ph.D., of the University of Pittsburgh School of Medicine. "We wanted to understand how factors such as depression or the baby blues, and weight concerns, might affect women's motivations to smoke after delivery."

"Conventional wisdom tells us that it should be easy to abstain if you have gone without cigarettes for six months or so," Levine added. "But it is clear that many women who say they don't want to start smoking again end up doing just that."

Even women who quit smoking for the health of the baby they are carrying may not realize that nicotine can be passed to infants through breast milk, and that secondhand smoke can cause colds, bronchitis, asthma, and other respiratory ailments among children.

The research appears in the October 2006 edition of the Annals of Behavioral Medicine.