Previous research has shown that babies still in their mothers’ wombs regularly stretch, swallow and even hiccup. Recent observations have found another item to add on the list – yawning. The doctors involved in the research that identified yawning in fetuses believe this could serve as a new indicator for assessing an unborn baby’s health index.

I was just kidding about the bored part in the title, though fetuses might very well yawn of boredom; it’s not like they’re going anywhere and, after all, we’re talking about nine freakin’ months trapped in-utero. Why do we yawn anyway? Well, first of all, yawning is a physiological mechanism that is totally uncontrollable, expressed by all classes of mammals,  and is correlated by a variety of neurochemical changes in the brain. You’d think that such a common behavior would be fully explain by 21st century science, but the truth is, despite several theories that claim they have the answer, scientists aren’t sure what causes or what’s the purpose of yawning.

Yawning fetus. (c) Durham and Lancaster Universities

Yawning fetus. (c) Durham and Lancaster Universities

A study from 2008 published in the journal Evolutionary Psychology found that yawning is linked with body temperature, and acts a regulator. Back then the researchers of the respective paper proved their theory by raising the ambient temperature in a cage where several parrots were sited. As temperatures rose, they found that the birds were twice as likely to  engage in rapid and continuous opening and closing of the beak, which acts to flap membranes in the throat and thereby increase evaporative cooling. Back to babies, though.

Researchers from Durham and Lancaster Universities studied 15 healthy fetuses using 4D scans that render real-time snapshots of what’s going inside the womb. The image on the left clearly shows a fetus yawning, for instance, or is it? How did the researchers distinguish actual yawning from mere mouth opening? The scientists closely examined all events where a mouth stretch occurred in the fetus, and using their newly developed criteria, the research team found that over half of the mouth openings observed in the study were classed as yawns.

The studied fetuses were between 24 to 36 weeks gestation, of which eight female and seven male. The researchers found that yawning declined from 28 weeks and that there was no significant difference between boys and girls in yawning frequency.

Despite a general scientific consensus has yet to be reached on the importance and function of yawning,  the scientists  suggest that yawning could be linked to fetal development, and as such with its health.

The results of this study demonstrate that yawning can be observed in healthy fetuses and extends previous work on fetal yawning.  Our longitudinal study shows that yawning declines with increasing fetal age.

 “Unlike us, fetuses do not yawn contagiously, nor do they yawn because they are sleepy.  Instead, the frequency of yawning in the womb may be linked to the maturing of the brain early in gestation”, said lead researcher, Dr Nadja Reissland, of Durham University’s Department of Psychology,

“Given that the frequency of yawning in our sample of healthy fetuses declined from 28 weeks to 36 weeks gestation, it seems to suggest that yawning and simple mouth opening have this maturational function early in gestation.”

The video below shows a 30 week old fetus scanned with ultrasound 4D imaging.

Findings were published in the journal PLOS ONE.