Women in the county are far less likely to quit smoking during pregnancy than anywhere else in the East Midlands.
Just 53 of the 185 women who aimed to kick the habit in the period from April to September last year achieved their goal.
The figures rank NHS Northamptonshire bottom of the nine health trust areas in the East Midlands.
NHS Nottingham got the highest with 60 per cent.
They also place the county health body 15th worst for pregnant women quitting smoking of 160 areas in the country.
A spokesman for NHS Northamptonshire pointed out that the body helped a total 2,390 people quit smoking in the same period, an increase of 200 on the same period the year before.
But he admitted helping pregnant women was difficult.
He said: “Supporting pregnant women to quit smoking is challenging but remains a priority for NHS Northamptonshire.
“Current figures have found that for this period only 29 per cent of the pregnant women successfully quitting smoking compared to the England figure of 43 per cent.
“Additional investment into services to reduce smoking in pregnancy has, however, seen good progress being made, with the smoking prevalence rate for Northamptonshire reducing from 18 per cent in 2008-09 to 14.9 per cent in 2010-11.
“The local Stop Smoking Service has a team of specialist advisors who are skilled and trained to provide support to all smokers, including pregnant women and their families.”
The NHS regularly runs advertising campaigns aimed at stopping pregnant women smoking. It says smoking puts carbon monoxide in the blood and restricts the flow of oxygen to the baby.
Jane Collins, 72, of Gordon Street, Wellingborough, admits she smoked up to 30 a day when she was pregnant.
The retired school cleaner, who quit five years ago, said: “There wasn’t the knowledge back then and people weren’t told so much not to smoke with a baby.
“I think many mothers still do today, you see them in the town centre.
“To quit smoking you have to want to yourself, not just because someone else wants you to.”
The NHS Stop Smoking Helpline on 0845 6013116.