New research suggests that the harmful effects of smoking during pregnancy may be reflected in the facial movements of mothers' unborn babies.

Researchers at Durham and Lancaster universities found that fetuses whose mothers were smokers showed a significantly higher rate of mouth movements than the normal declining rate of movements expected in a fetus during pregnancy. These findings add weight to existing evidence that smoking is harmful to fetuses as they develop in the womb and warranted further investigation.

"Fetal facial movement patterns differ significantly between fetuses of mothers who smoked compared to those of mothers who didn't smoke," Dr. Nadja Reissland, lead author of the study, said in a statement.

For the study, researchers observed 80 4-d ultrasound scans of 20 fetuses, to assess subtle mouth and touch movements. Scans were taken at four different intervals between 24 and 36 weeks of pregnancy.

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.

The study also found some evidence of a bigger delay in the reduction of facial touching by fetuses whose mothers smoked, compared to the fetuses of non-smokers, but the researchers said this delay was less significant.

"Our findings concur with others that stress and depression have a significant impact on fetal movements, and need to be controlled for, but additionally these results point to the fact that nicotine exposure per se has an effect on fetal development over and above the effects of stress and depression," Reissland said. "A larger study is needed to confirm these results and to investigate specific effects, including the interaction of maternal stress and smoking."

The researchers stressed that their research was a pilot study and that larger studies were needed to confirm and further understand the relationship between maternal smoking, stress, depression and fetal development.

The findings are detailed in the journal Acta Paediatrica.