The dramatic 4D ultrasound photos of unborn babies “grimacing” and “suffering” in the womb as their mothers smoked cigarettes made a high-profile splash on social media earlier this week.

The photos come from a study published online recently in the medical journal Acta Paediatrica by a team of British researchers.

But do those photos actually show fetuses in distress because of their mother’s smoking?

Maybe. Or maybe not. There’s no way of knowing from the photos — or from the study — what those unborn babies (photographed between weeks 24 and 36 of pregnancy) are feeling, as experts for the United Kingdom’s National Health Service (NHS) explain on the organization’s “Behind the Headlines” website.

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“While smoking is certainly known to be harmful in pregnancy, the researchers [and the media] may be reading too much into these images by claiming they show ‘grimaces’ or expressions of pain in response to smoking,” the NHS experts write.

Important limitations

Here, in their words (and with British spellings), are some of the reasons why we should hold off jumping to any conclusions about those images:

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 smoked 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. … 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. … Another limitation is the potential influence of confounding — that is, any differences may not necessarily be a direct effect of smoking, but could the the result of the influence of other factors … such as socioeconomic factors, whether the father smoked, or other health and lifestyle factors in mother, such as diet, physical activity, [body mass index] and alcohol intake.

“The images are powerful and provoke an emotive result in most people, as the baby appears to be in distress,” the NHS experts add. “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.”

What the evidence does say

But, as the experts also stress, pregnant women have plenty of compelling and evidence-based reasons to not smoke — and to avoid being exposed to secondhand smoke:

You will have less morning sickness and fewer complications in pregnancy

You are more likely to have a healthier pregnancy and a healthier baby

The risk of stillbirth is reduced

You’ll cope better with the birth

Your baby is less likely to be born too early

Your baby is less likely to be born underweight

The risk of cot death is reduced

An abstract of the pilot study can be found on the Acta Paediatrica website. You can read the NHS’ full discussion of the study on the agency’s “Behind the Headlines” website. It’s a great site to bookmark for clear-headed examinations of studies that hit the media headlines.