Yawning is one of the most mysterious and shared behaviors in the animal kingdom. You know the scene: in the subway or in the office, all it takes is one person opening their mouth wide for a chain reaction to begin. Until now, researchers considered this exchange as a complex social mechanism requiring a certain cognitive maturity. It was known that babies in the womb yawned, but it was thought to be a simple mechanical reflex, a kind of training of the jaw muscles unrelated to the environment.
However, new research has shaken up these certainties. Scientists wanted to know if the fetus, although isolated in its bubble of amniotic fluid, could be sensitive to its mother’s state of fatigue or physiological signals. The experiment brought together 38 pregnant women during their third trimester of pregnancy. The protocol was simple, but rigorous: while the mothers watched videos of people yawning, making simple mouth movements or even impassive faces, the researchers examined the babies’ reactions in real time using ultrasound imaging. As might be expected, the yawning videos provoked a reaction among mothers: around 64% of them yawned at least once while watching them, while almost none yawned with the other types of videos.
The results, reported by Smithsonian Magazine, indicate that around 53% of fetuses yawned when their mothers were exposed to yawning videos. Even more impressive: the response was not long in coming. On average, the future baby’s mirror yawn occurred about a minute and a half after the mother’s. The researchers also noted a direct correlation: the more frequently the mother yawned, the more the fetus tended to imitate her.
The study highlights a form of early synchronization that goes beyond just basic biology. For Giulia D’Adamo, neuroscientist at the University of Parma and lead author of the study, during pregnancy “it’s all about setting up for what happens next“. This suggests that the foundations of our social interactions and empathy may be formed long before our first cry. The fetus would therefore not be a passive spectator, but a being already connected to the rhythms and expressions of its mother.
Why do we really yawn?
How does this signal cross the placental barrier? Scientists are exploring several avenues. The first is hormonal: the mother’s yawn could release certain substances into the blood which, once transmitted to the fetus, would trigger the same reaction. Another, more surprising hypothesis suggests that the fetus might sense the physical vibrations or pressure changes caused by its mother’s deep inspiration. An invisible, but very real, form of communication that would already take place in the womb.
Beyond the mother-child connection, this discovery rekindles the debate on the very usefulness of yawning. It was long believed that it was used to oxygenate the blood, but this theory is now contested. Another hypothesis states that this is a thermostat function. Yawning helps cool the brain when its temperature rises too much, thus promoting alertness. For a fetus, yawning could therefore be a way of regulating its developing nervous system.
Another fascinating avenue links yawning to brain cleansing. Recent research suggests that it may act as a hydraulic pump for the glymphatic system, responsible for removing toxins from the brain. As neurologist W. Christopher Winter points out, “LYawning is a lot like your brain saying, “If you’re not going to sleep to engage that glymphatic system, then we’re going to turn on the emergency pump.”“.
Ultimately, whether to cool our internal processor, clean our cells, or strengthen social bonding, yawning remains one of the common threads of our humanity. Knowing that this link is established in the last weeks of pregnancy adds an additional dimension to this movement which has become almost trivial.
