When mothers-to-be smoke, the effects can be seen in the tiny movements of their fetuses, according to researchers examining high-resolution ultrasound scans. 

Healthy fetuses start out by exploring their new limbs and body parts—touching their head and face and moving their mouth in a bunch of shapes. But these movements become less frequent as their central nervous system (which controls movement) develop. 

A U.K. team led by Nadja Reissland of Durham University observed thousands of subtle mouth and touch movements in 80 4D ultrasound scans of 20 fetuses: Four belonged to women who smoked an average of 14 cigarettes a day, while the other 16 were carried by non-smokers. The scans were taken at four different intervals between 24 and 36 weeks of pregnancy, and the women also filled out questionnaires about stress and depression. The fourth dimension in 4D is time. “Technology means we can now see what was previously hidden, revealing how smoking affects the development of the fetus in ways we did not realize,” study co-author Brian Francis of Lancaster University says in a news release. "This is yet further evidence of the negative effects of smoking in pregnancy."

All of the babies were born healthy. However, the fetuses of mothers who smoked showed a significantly higher rate of mouth movements—compared to the normal declining rate of movements expected in a fetus during pregnancy. They also found evidence of a delay in the reduction of facial touching by fetuses whose mothers smoked. In this extended sequence of movements, the fetus whose mother is a smoker is on top, and a fetus whose mother is a non-smoker is on the bottom:

The researchers think the reason for these reactions might be that the fetal central nervous system didn’t develop at the same rate and in the same manner as in fetuses of pregnant mothers who didn’t smoke. "The images suggest that fetuses in smokers are less mature in their behavior," Reissland tells USA Today. Previous work have indicated a delay of speech processing abilities in infants exposed to smoke prenatally. 

"Our findings concur with others that stress and depression have a significant impact on fetal movements, and need to be controlled for,” Reissland says in a university statement, “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.”

The results of this pilot were published in Acta Paediatrica earlier this month. They’ll need to be confirmed with a larger study, which could also further examine specific effects. 

Image: Nadja Reissland, Durham University