The majority of women fail to give up smoking during pregnancy even when given specialist counselling, researchers have found.
The study says pregnant smokers are failing to kick their habit
The Glasgow University team discovered that despite the harmful effects smoking can have on unborn babies, most mums-to-be struggle to quit.
It is estimated that a third of pregnant women smoke.
Researchers looked at the impact one-to-one counselling by midwives had on pregnant smokers.
A total of 762 pregnant women who were regular smokers when they became pregnant took part in the study.
All of them were given standard health promotion information, but 351 were also offered up to five motivational interviews at home with specially-trained midwives.
The researchers measured the women's levels of cotinine - a by-product of nicotine found in the blood and saliva - to check the results in women who said they were quitting or cutting down on cigarettes.
No significant differences in changes to smoking behaviour were found between the group given standard health information - the controls - and those given counselling as well.
In those offered counselling, 17 (4.8%) stopped smoking, compared to 19 (4.6%) in the control group.
Fifteen (4.2%) women in the counselling group cut down on the number of cigarettes they were smoking, compared to 26 (6.3%) in the control group.
The researchers said: "A good standard of motivational interviewing provided by midwives did not help women who were smoking at maternity booking to stop smoking."
They said that behavioural interventions alone in heavily-addicted pregnant women were unlikely to be effective enough to provide good value for money.
Nicotine replacement therapy is often effective in helping smokers stop, but is not routinely recommended during pregnancy.
But the researchers said that midwives could provide close supervision of nicotine replacement in women who would not be able to stop otherwise, once its safety and effectiveness had been examined.
The research was published in the British Medical Journal.