Pregnancy and child

Yawning while in the womb may offer insight into baby’s health

Yawning in the womb could be used as a “baby health indicator”, The Guardian reported today. It said ultrasound scans that catch unborn babies ‘yawning’ may help doctors monitor normal development.

The story is based on a small study that used real-time ultrasound scans (so called 4D scans) to monitor the faces of foetuses in the womb. The scans did capture some remarkable footage of facial movement, which the researchers interpreted as a ‘yawn’. This suggests that healthy foetuses do indeed yawn, more so in the early stages of pregnancy.

This is a fascinating study, with some remarkable footage of foetuses ‘yawning‘ at different gestational stages. However, it is not clear whether all experts agree on what would be considered a foetal ‘yawn’, and the researchers developed their own definition (a foetus’s yawn could easily be in fact, a foetal belch).

To suggest that yawning in the womb is a sign of foetal health, is premature.

The researchers’ speculated that foetal yawning may be related to development of the brain or central nervous system. However, this is just a theory that would need to be tested in further research. 

Where did the story come from?

The study was carried out by researchers from the University of Durham and Lancaster University. It was funded by both of these universities.

The study was published in the open-access, peer-reviewed journal PLoS One.

Not surprisingly, due to the striking images accompanying the study, it was covered widely by the papers, some of which overplayed its significance in terms of foetal health.

The Guardian in particular overstated the possibility, suggested by researchers, that ultrasound scans of babies yawning could one day be used by doctors to monitor normal development in the womb. It’s worth noting that, in their study, the researchers used specialised 4D ultrasound to detect foetal mouth movements and not the standard ultrasound scans used routinely in pregnancy check-ups.

What kind of research was this?

The researchers say that the development of yawning is poorly understood, with several differing theories as to its function.

They point out that although some researchers suggest that foetuses yawn, others disagree, arguing that it is simple mouth opening rather than yawning.

They also point out that research suggests that premature babies yawn more frequently than babies born at term, and primary school children yawn more frequently than those in nursery.

In this study, the researchers aimed to establish the frequency and development of foetal yawning over the second and third trimesters of pregnancy, compared with simple mouth opening.

Yawning commonly refers to an involuntary intake of air by opening the mouth, but this definition cannot be applied to foetuses in the womb since they obtain oxygen via the placenta.

In this study, foetal yawning was defined based on ‘mouth opening with the jaw dropping‘ and the relative time taken for the mouth to reach full opening compared with the entire time the mouth was open. Whether this amounts to a proper yawn is debatable.

What did the research involve?

The researchers made videos of 15 healthy foetuses (eight girls and seven boys), using 4D full frontal or facial profile ultrasound recordings of the foetal face and upper body. They scanned the foetuses four times – at 24, 28, 32 and 36 weeks’ gestation. 

Each observation period was 10 minutes’ long, starting when the full face was visible.

They observed all events where they say a ‘mouth stretch‘ occurred; mouth stretch being defined as the mandible (jaw) being pulled down.

They timed two stages of the ‘mouth opening event‘ – from mouth opening start to maximum opening, and from maximum opening to closure.

They defined a ‘yawning event’ as mouth openings where the time taken to maximum opening of the mouth was more than half of the total time the mouth was open, while the rest were labelled as non-yawn mouth openings.

They say that this definition of yawning, in which yawning is a slow opening of the mouth and a faster return to the initial position, is supported by experts.

The women who participated were all first-time mothers who were 27 years old on average, and who had been recruited by midwives in an antenatal unit. At birth, all were rated as healthy by a paediatrician.

What were the basic results?

The researchers based their results on 58 scans (two scans could not be included because the complete cycle of mouth movements could not be observed).

  • In total they observed 56 yawns and 27 non-yawn mouth openings.
  • The rate per hour for yawns was 6.02 and for non-yawns was 2.79.
  • There was a ‘strong decline’ in the average frequency of both yawns and non-yawns as gestational age increased.
  • The number of yawns observed declined from 28 weeks’ gestation, the number of non-yawns from 24 weeks.
  • There was no difference in the number of yawns or non-yawns between male and female foetuses.

How did the researchers interpret the results?

The researchers say that yawning can be reliably distinguished from other forms of mouth opening in foetuses and that there is potential to use yawning as an index of healthy foetal development.

They also suggest that their research could support the suggestion that yawning is related to the development of the central nervous system and maturation of the brain.


This is an interesting study, but the question of why (or indeed, if) foetuses ‘yawn’ is still uncertain. It should be noted that the researchers created their own definition of a foetal yawn, and had tested it previously to distinguish between foetal yawns and non-yawns.

Whether all experts agree on what constitutes a foetal yawn as opposed to a non-yawn is not clear.

To suggest that foetal yawning could be used as a measure of healthy foetal development is premature.

In order to examine this issue, a far larger study looking at the relationship between foetal yawns and foetal health or pregnancy outcomes would be required.

Still, aside from any future health applications, the researchers did manage to capture a series of compelling and remarkable ‘real-time’ images of foetuses in the womb.

Analysis by NHS Choices. Follow Behind the Headlines on twitter.

NHS Attribution