Researchers from the UK’s Durham and Lancaster University have found visual evidence of the effects of smoking on fetuses in a mother’s womb.

4D ultrasound images appear to show babies frowning and touching their mouths when their mother smokes a cigarette. This is unusual, as fetuses are known to move their mouths and touch themselves less as they become more developed.

The university study, which was small and may need to expand to get more firm results, indicates that the fetuses of smokers may have a higher risk for delays in central nervous system development.

The University of Durham's Dr Reissland told the Telegraph that "A larger study is needed to confirm these results and to investigate specific effects, including the interaction of maternal stress and smoking."

The study also noted that "Four of the fetuses belonged to mothers who smoked an average of 14 cigarettes per day, while the remaining 16 fetuses were being carried by mothers who were non-smokers. All fetuses were clinically assessed and were healthy when born."