If you were in any doubt about what smoking does to an unborn baby, take a look at these shocking 4D ultrasound pictures.
In the scans, the babies appear to grimace in the womb when their mother inhale, and some even hold their faces.
It's widely known that smoking during pregnancy increases the risk of premature birth, respiratory problems and even cot death.
But now scientists have shown the distress caused to the babies themselves inside the womb – and are using the images to encourage mothers who are struggling to give up.
Dr Nadja Reissland monitored 20 mothers attending the James Cook University Hospital in Middlesbrough, four of whom smoked an average of 14 cigarettes a day.
After studying their scans at 24, 28, 32 and 36 weeks, she detected that foetuses whose mothers smoked continued to show significantly higher rates of mouth movement and self-touching than those carried by non-smokers.
Foetuses usually move their mouths and touch themselves less as they gain more control the closer they get to birth.
The pilot study, which Dr Reissland hopes to expand with a bigger sample, indicated that babies carried by smokers may have delayed development of the central nervous system.
The research, conducted by Durham and Lancaster University, is published in the journal Acta Paediatrica.
Dr Reissland, from Durham's Psychology Department, said: "A larger study is needed to confirm these results and to investigate specific effects, including the interaction of maternal stress and smoking."
She believed that videos of the difference in pre-birth development could help mothers give up smoking.
But she was against demonising mothers and called for more support for them to give up.
Currently, 12 per cent of pregnant women in the UK smoke but the rate is over 20 per cent in the Durham, Darlington and Tees area.
All the babies in Dr Reissland's study were born healthy, and were of normal size and weight.
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