Mothers usually quit smoking in pregnancy, but they are more likely to pick up the habit again after their baby is born if they feel stressed, according to a recent study.

Researchers at the University of East Anglia found that while more women quit smoking during pregnancy than any other time, but as many as 90 percent light-up again within a year of their baby being born. They believe that the stress of caring for a newborn, sleepless nights, social pressure, and the idea that they no longer need to protect the baby -- all contribute to relapse.

"We found that many women see smoking as a way a coping with stress. They also believe that physiological changes influence cigarette cravings, and that they no longer need to protect the baby from smoking's harmful effects," Dr. Caitlin Notley, lead researcher of the study, said in a statement. "This is particularly true among women in lower socioeconomic groups."

For the study, researchers studied interviews with more than 1,000 new mothers. The study sought to find out what factors influence women to start smoking again after childbirth, as well as what things make it easier or more difficult to stay smoke free.

"One of the most striking things that we found is that women's beliefs about smoking are a major barrier to remaining smoke free," Notley said. "Many felt that smoking after the birth of their child was acceptable provided they protected their babies from second-hand smoke. Their focus is, admirably, on the health of the baby, but they often do not think about the long term health consequences for themselves as mothers."

Supportive partners were cited as key to remaining smoke free, along with personal praise from health professionals.

The findings are detailed in the journal Addiction.