Smoking among pregnant women has been known to have unwanted consequences to the babies when they are born but the harmful effects of the habit can also be seen even on unborn babies. Using 4D ultrasound, a new research shows the effects of smoking on the movements of the tiny faces of unborn babies.

For the new research, which was published in Acta Paediatrica, Brian Francis, from Lancaster University, and colleagues involved 20 pregnant women, four of whom smoke an average of 14 cigarettes per day, and 16 non-smokers.

The researchers performed high-definition 4D ultrasound on these women's unborn babies between 24 and 36 weeks gestation over a period of three months and found distinct differences in the fetuses whose mothers smoke.

The researchers in particular found that the unborn babies of smoking mothers have significantly higher rate of mouth movements compared with those of non-smoking mothers and this suggests that those carried by smoking mothers did not develop central nervous system, which control the movement, in the same manner and rate as the other fetuses.

The babies of mothers who smoked were more likely to touch their face often. The researchers also found that the stress level of the mothers had an effect on the baby's movement as the babies moved their mouths and touched their faced more frequently when the mothers experiences higher stress levels.

"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," said Nadja Reissland, of Durham University.

The research shows that the mothers who smoke delay the development of their unborn baby's central nervous system. It is also hoped that the new study could help encourage mothers to give up smoking while they are pregnant. The study researchers, however, said that a bigger study is required to determine if their findings are reliable.

The Centers for Disease Control and Prevention (CDC) said that during pregnancy, smoking raises the risk of low birthweight and preterm delivery and these could lead to health problems. Earlier studies have also showed that infants who were exposed to smoking prior to birth tend to have delayed speech processing abilities.

In adults, smoking is also associated with a number of unwanted health problems including increased risks for lung cancer.