Mothers who manage to quit cigarettes while pregnant are more likely to resume smoking after their baby is born if they are stressed, a new study has found.

The idea that they no longer have to protect the baby also increases the likelihood that they will smoke again.

According to UK researchers, more women quit smoking during pregnancy compared to any other time, however as many as 90% will light up again within the first year of their baby's life.

"We wanted to understand why this happens, and identify ways of preventing it. This is important both for the health of the mother, as well as to stop children being exposed to second hand smoke, and because young people are more likely to start smoking if they grow up with smoking in the family," commented lead researcher, Dr Caitlin Notley, of the University of East Anglia.

The study set out to determine what influences women to take up smoking again and what makes it easier for them to stay off cigarettes.

The study found that women who saw smoking as a way of coping with stress were more likely to take up the habit again. Those who felt lonely, low and tired were also more likely to relapse.

Some also believed that they ‘no longer needed to protect the baby from smoking's harmful effects', Dr Notley said.

Furthermore, many women reported that cravings for nicotine, which had lessened or stopped during pregnancy, returned after the baby was born.

"In many women, the motivation to stop smoking was linked to their pregnancy, but they didn't see it as stopping for good and adopting a life without smoking. Relapse seemed almost inevitable where women admitted that they didn't quit for themselves," Dr Notley noted.

She also noted that social influences played a part. Some women said that their friends expected them to resume smoking and this influenced them to start again.

"One of the most striking things that we found is that women's beliefs about smoking are a major barrier to remaining smoke free. 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," Dr Notley pointed out.

The study also found that it was extremely difficult for women to stay off cigarettes if their partner smoked. However, having a supportive partner was seen as key to staying off cigarettes, along with personal praise from healthcare professionals.

"The majority of women who had successfully remained smoke free said that the support of their partner was a strong factor. Partners who gave up smoking, or altered their own smoking behaviours, were a particularly good influence. And those who helped ease the stress of childcare were also praised by women who had resisted the urge to light up," Dr Notley said.

Details of these findings are published in the journal, Addiction.