Pregnant women are more likely to stop smoking if they are given shopping vouchers as a financial incentive, according to scientists.

The study found that one-fifth of women in the scheme had stopped smoking by the time they gave birth, more than twice the rate achieved using traditional support services.

Prof Theresa Marteau, the study’s lead author at the University of Cambridge, said there was a compelling case to make financial incentives for smoking a routine part of antenatal services, but added that many found the idea of “paying people to do the right thing” unpalatable.

“It’s an inconvenient truth that the most effective intervention we’ve got is one that people don’t like,” she said. “One can call it patronising and take the moral high ground, but it is significantly more effective than anything else.”

Overall, 12% of women in England smoke throughout pregnancy, ranging from one in 200 (0.5%) in affluent areas smoking, to higher than one in four (27%) in the most deprived regions.

Babies of mothers who smoke are born, on average, 200g (7oz) lighter than those of non-smokers, are more likely to be born prematurely and have higher rates of asthma and infections, meaning that smoking during pregnancy is a major cause of health inequality from birth.

The study, published in the journal Addiction, was carried out in antenatal clinics in Chesterfield, Derbyshire, which is an area of high social deprivation.

Two out of five women who attended the clinic – 239 women in total – enrolled into the financial incentive scheme. At each visit, the women were asked if they had smoked since the last visit and were given a carbon monoxide breath test to check if they had smoked in the preceding few hours. If they had not smoked, they were given a shopping voucher – the first voucher was worth £8 and the value increased by £1 for each further visit, providing up to a maximum of £752 in vouchers.

Testing positive for smoking meant forfeiting the incentive and returning to the baseline £8 rate at the next visit.

The results, backed up by analysis of saliva and urine samples, showed that one in five of the women had quit by the time of delivery and 10% were still not smoking six months after the birth of their child. The previous year, fewer than 1 per cent had quit at the same time point, when women had been offered standard NHS support for stopping smoking.

In general, the NHS Stop Smoking services help around six in every 100 pregnant women to stop smoking, the researchers said, compared with more than 20 out of 100 by financial incentives.

The study showed that very few women “gamed the system”, with no evidence that anyone had falsely claimed to smoke before enlisting on the trial and only 10 women claiming vouchers by saying they had abstained between sessions when tests showed they had smoked.

Louise Silverton, director for midwifery at the Royal College of Midwives, said the research showed that financial incentives do increase the numbers of women who are able to successfully stop smoking. “Although financial incentivisation may be one way forward, it will be expensive, and alternative ways of stopping smoking in pregnancy also need attention,” she added.

Martineau said this view echoed that of the public, that it was preferable to spend money on education initiatives rather than direct incentives, but said that incentives were more cost-effective.

“A lot of people have this attitude of ‘why should the feckless poor who smoke their head off during pregnancy be rewarded’?” she said. “The fact is, nearly all pregnant women would prefer not to be smoking.”

Julie Hirst, public health principal at Derbyshire county council, said: “Smoking is very addictive and these women have done incredibly well to quit. The incentive scheme gave them that bit of extra help that made all the difference. As a council we are committed to extending this scheme to the other areas of Derbyshire where there is a higher than average prevalence of smoking in pregnancy.”

In total, £37,490 was spent on the financial incentive, which the researchers believe is likely to fall within the acceptable range of cost-effectiveness set by the National Institute for Health and Care Excellence (Nice).