Pregnancy and child

'4D' ultrasound shows effects of smoking on unborn babies

"Unborn baby shown grimacing in womb as mother smokes," is the somewhat misleading headline in The Daily Telegraph.

The news comes after researchers released dramatic images of babies in the womb taken using 4D ultrasound scanners. 4D scanners provide real-time moving images of babies in the womb.

Some newspapers have interpreted these images as showing distress caused by smoking. While smoking is certainly known to be harmful in pregnancy, the researchers may be reading too much into these images by claiming they show "grimaces" or expressions of pain in response to smoking.

The scans came from a small pilot study that showed differences between the movements of the unborn babies of four mothers who smoked, compared with the unborn babies of 16 non-smokers.

The paper says unborn babies touch their faces and move their mouths more in the earlier stages of their development, making these movements less often as they mature.

This study scanned babies between weeks 24 and 36 of pregnancy, and showed that babies carried by women who smoked appeared to move their mouths and touch their faces more than non-smokers' babies.

The implication is that this is a sign of slower development as a direct result of maternal smoking. But this has not been proven.

This study had a very small sample size, including just four smokers. And we don't know whether these observed differences in movement actually have any meaning in terms of the ongoing development of the unborn baby, or during infancy or childhood.

Still, we don't need any new research to tell us that smoking in pregnancy is harmful. Every cigarette you smoke contains more than 4,000 chemicals that will harm your baby.

Protecting your baby from tobacco smoke is one of the best things you can do to give your child a healthy start in life. It's never too late to stop smoking.  

Where did the story come from?

The study was carried out by researchers from Durham and Lancaster universities and James Cook University Hospital in Middlesbrough. We do not know who funded the study.

It was published in the peer-reviewed medical journal Acta Paediatrica.

Emotive images from the study were widely reproduced in the media. The Daily Telegraph suggested that the baby in the images was "grimacing" in response to cigarette smoke, while the Daily Mirror says the "dramatic pictures" show babies "suffering in the womb".

But the mother would not have been smoking in the hospital while being scanned, and we don't know the significance of the facial movements shown in the images, much less whether they represent suffering.

A case could be made that using the images to frighten mothers into quitting would be justifiable for the greater good, but it also wouldn't be entirely truthful or transparent.  

What kind of research was this?

This was a pilot observational study of a small number of pregnant women. It intended to see whether ultrasound scans could provide reliable information on subtle foetal movements (rather than asking mothers to count movements), and also see whether there are differences seen in the unborn babies of mothers who smoke.

This type of study can point to differences between different groups, but it cannot show what caused the differences. The researchers say a bigger study is needed to see if their findings are reliable and investigate them further. This study also can't tell us what the differences in movements mean for the development of the babies.

What did the research involve?

The researchers used 4D ultrasound to scan the unborn babies of 20 mothers, four of whom smoked. The babies were scanned four times from 24 to 36 weeks of pregnancy for 15 to 20 minutes at a time.

The scan is known as 4D because it provides detailed 3D-like moving images, time being the fourth dimension. 

Recordings were analysed for the numbers of times the babies moved their mouths and touched their faces.

The women filled in questionnaires at each scan to say how stressed they were feeling. They also completed a widely used depression questionnaire called the Hospital and Anxiety Depression Scale.

The ultrasound scans took images every half a second, producing detailed pictures of the babies' faces through time. Some scans were double-checked independently to confirm that the movement counts were accurate.

The researchers used standard methods to analyse the differences between smoking and non-smoking groups and how they changed over the four scans. They adjusted their results to take account of the babies' gestational age and sex, and the mothers' age, stress level and depression symptoms.

What were the basic results?

Babies whose mothers smoked (14 cigarettes a day on average) moved their mouths more often than babies whose mothers were non-smokers. This was true at the start of the study, and the gap widened as the study went on.

Babies whose mothers did not smoke reduced their number of mouth movements from their first to last scan by about 3% a week. This happened more slowly for babies whose mothers smoked, at 1.5% a week.

The results were less clear-cut for the number of times babies touched their faces. Researchers said the difference between the two groups was "borderline [statistically] significant", meaning they cannot be sure this was not down to chance.

However, the direction of the effect was similar – babies whose mothers smoked tended to touch their faces more often, and there was a decline in movement in both groups as the babies grew.

Mothers' stress levels also affected the baby's movements. Babies moved their mouths and touched their faces more often when their mothers reported higher stress levels.

All babies were born healthy, and there were no significant differences recorded between the babies born to smokers and non-smokers.

How did the researchers interpret the results?

The researchers say their study shows that the scanning technique they used provides a more sensitive way of assessing differences in babies' movements before they are born, compared with methods such as asking mothers to record how often they feel the baby move.

They say the comparison between smoking and stress levels shows that "smoking appears to be more important than stress" in terms of how it affects the baby's movements.

While they cannot be sure why the differences in face touching arise, the researchers suggest the babies may touch their faces to soothe themselves in a way that young infants have been seen to do after birth.

They also suggest the differences in mouth movements and face touching could be down to the rate at which the baby's central nervous system (brain and spinal cord) matures. Babies whose mothers smoke are thought to have slower-maturing nervous systems.


This pilot study looked at whether ultrasound scans could be a reliable way of assessing foetal movements. It then looked at whether movements differ between babies whose mothers smoke and those who do not.

The study found babies whose mothers smoked moved their mouths more often, and the rate at which they reduced their mouth movements was slow compared with babies whose mothers didn't smoke.

The main limitation of this study was its size – only four smokers and 16 non-smokers were included. This means the results are more likely to be down to chance than in a bigger study. We can't be sure that these results apply to all babies of smokers and non-smokers, and a bigger study is needed to confirm the results.

A further point is that if there are real differences between the movements of babies whose mothers smoke or don't smoke, we can't say exactly why these differences arise or what they mean for the baby.

The researchers have suggested reasons for the differences in movements, but this type of study is not designed to look at the reason behind the differences.

We need more research to investigate whether the differences seen in this study do represent slower development of the baby's nervous system, and whether they could have any meaning for the continued growth and development of the infant or child.

Another limitation is the potential influence of confounding – that is, any differences may not necessarily be a direct effect of smoking, but could be the result of the influence of other factors. The study did take into account the baby's gestational age and sex, or the mother's age, stress levels and depression symptoms, for instance.

However, other factors could have influenced the results, such as socioeconomic factors, whether the father smoked, or other health and lifestyle factors in the mother, such as diet, physical activity, BMI and alcohol intake. 

The photographs released to the media are from two 10-second scans of 32-week-old babies, one taken from a woman who smoked and one from a non-smoker. They are described as "illustrative". The first shows the baby covering its face with both hands, while the second shows the baby with a hand to its mouth.

The images are powerful and provoke an emotive result in most people, as the baby appears to be in distress. But it's important to bear in mind that these images may not be representative of the approximately 10 to 13 hours of scans taken. We cannot tell whether the babies pictured were distressed, contented, or showing another emotion.

Despite the limitations of this study, it is already well established that smoking during pregnancy has various harmful effects, both to mother and baby.

This small study found there may be differences in the movement of unborn babies of smoking and non-smoking mothers. Whether there are true differences, and whether they have any meaning or implications in terms of the baby or child's ongoing development, is something that needs to be examined in further larger studies.

NHS Attribution