The harmful effects of smoking during pregnancy on unborn babies may be seen in tiny movements in their faces using 4D ultrasound scans, British research has found.
Pregnant women have long been urged to give up cigarettes because they heighten the risk of premature birth, respiratory problems and even cot death.
Now researchers believe they can show the effects of smoking on babies in the womb - and use the images to encourage mothers-to-be to give up.
Dr Nadja Reissland has studied 4D scan images and recorded thousands of tiny movements in the womb.
She monitored 20 women 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 the closer they get to birth as they gain more control. The pilot study indicated that babies carried by smokers may have delayed development of the central nervous system.
The research, conducted by Durham and Lancaster universities, 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-to-be to give up smoking.
But she was against demonising smokers and called for more support for them to give up.
All the babies in her study were born healthy, and were of normal size and weight.
Dr Reissland, who has an expertise in studying foetal development, thanked the mothers who took part in her study, especially those who smoked. "I'm really grateful, they did a good thing," she said. "These are special people and they overcame the stigma to help others."
Co-author Prof Brian Francis, of Lancaster University, added: "Technology means we can now see what was previously hidden, revealing how smoking affects the development of the foetus in ways we did not realise. This is yet further evidence of the negative effects of smoking in pregnancy."
Studies have shown that lighting up also reduces sperm count, harms egg quality, hastens the menopause and increases the dangers of premature birth and the need for caesarean sections.
It also reduces the chances of a woman becoming pregnant because it undermines the ability of fertilised eggs to implant in the lining of the womb, according to another study out today.
According to a report published in AFP in 2014, in Australia, 14.5 per cent women report smoking while pregnant, with one in six quitting before their baby's birth. But the real number of smokers could be a lot higher, the authors noted, "as up to 25% of pregnant smokers do not disclose their smoking status, often because of the social stigma".