Le bâillement, du réflexe à la pathologie
Le bâillement : de l'éthologie à la médecine clinique
Le bâillement : phylogenèse, éthologie, nosogénie
 Le bâillement : un comportement universel
La parakinésie brachiale oscitante
Yawning: its cycle, its role
Warum gähnen wir ?
Fetal yawning assessed by 3D and 4D sonography
Le bâillement foetal
Le bâillement, du réflexe à la pathologie
Le bâillement : de l'éthologie à la médecine clinique
Le bâillement : phylogenèse, éthologie, nosogénie
 Le bâillement : un comportement universel
La parakinésie brachiale oscitante
Yawning: its cycle, its role
Warum gähnen wir ?
Fetal yawning assessed by 3D and 4D sonography
Le bâillement foetal
mystery of yawning 

mise à jour du
30 novembre 2017
Developmental of Normal Fetal movements
Springer 2015
Seemingly Trivial Fetal Motions:
Yawning and Hiccups
Alessandra Piontelli
Florinda Ceriani, Isabella Fabietti, Roberto Fogliani,
Elisa Restelli, and Alessandra Kustermann
Department of Maternal/Fetal MedicineClinica Mangiagalli,
Fondazione IRCCS Ca' Granda, Ospedale Maggiore Policlinico,
University of Milan, Italy


Tous les articles consacrés au bâillement foetal
Fetal yawning: all publications
 Bâillements du foetus: la naissance d'un comportement révélée par l'échographie 4D
Fetal yawning : a behavior's birth with 4D US revealed
Video de bâillement foetal à 23 semaines en Echo 4D
autres photos de bâillements foetaux
Video de bâillement foetal à 13 semaines en Echo 4D
Sonography Edited by: Kerry Thoirs
Fetal Yawning Olivier Walusinski
Chapter 18 Pages 325-332
Development of Fetal Yawn Compared with Non-Yawn Mouth Openings from 24-36 Weeks Gestation. Reissland N
Development of Normal Fetal Movements The first 25 weeks of Gestation Piontelli A

Yawning: A Brief Survey of the Main Possible Explanations
Yawning is a universal phenomenon shared by most vertebrate species from fetal life to old age.
Yawning is a common symptom of several illnesses, ranging from various pathologies of the central nervous system to diabetes and diseases of the liver and the adrenals, and as such has been studied predominantly in relation to these. Spontaneous yawns, however, have intrigued many over the centuries and numerous theories have been advanced as to why we yawn ordinarily. Up to this day, however, the function of spontaneous yawns remains unexplained.
Recently yawns have seen a revival of interest due principally to the work of Robert Provine, a neuroscientist professor of psychology at the University of Maryland, Baltimore [1], and of Olivier Walusinski, a French country doctor with a wide experience in many fi elds of medicine including obstetrics and ultrasound. Walusinski founded "Chasmology," a new discipline, deriving its name from the Greek khasma, meaning opening wide, and brought yawns to the limelight. Besides his own publications, all kinds of useful information and a very thorough biography can be found on his website [2,3].
These experts are not the only ones who have wondered why we yawn, given that as many as nearly 20 hypotheses have been formulated. The main theories put forward to explain the phenomenon are briefly the following. Respiratory and circulatory hypotheses date back to Hippocratic times when scholars believed that yawning removed "bad air" from the lungs and increased oxygen circulation in the brain. A modern derivation of these theories claims that yawning occurs when oxygenation is low either in the blood or brain or both. Robert Provine dispelled once and for all the oxygenation theory. Provine firstly noted that people do not yawn more frequently when they exercise. By means of experimental evidence, he then asked his subjects to inhale air with higher than normal levels of CO 2 and recorded that they did not yawn. On the contrary when the subjects inhaled unadulterated oxygen levels, spontaneous yawning was not inhibited [4]. This theory, however, continues to crop up from time to time.
Another hypothesis , the arousal theory, claims that we yawn when we feel drowsy either before or after sleep in order to keep us awake or help us to wake. However, again, experimental evidence proved the theory wrong. In fact, the contrary is true; yawning is triggered by states of drowsiness and low vigilance [5,6].
The state change hypothesis, put forward as a possible explanation by Provine, is based on the undoubted fact that multiple behavioral state shifts are associated with yawning. According to him yawning may facilitate or even trigger these transitions [7,9].
The boredom, sleepiness theory simply takes into account that we yawn when sleepy or bored. However, people also yawn in other circumstances, such as when waking up or being overwhelmed by anxiety [10,11]. Nevertheless, this theory too remains popular.
The cooling the brain hypothesis claims that humans and animals yawn in order to lower the temperature of the brain, thus remaining (similarly as in the arousing theory) alert and less vulnerable to possible perils [12].
The social/communication hypothesis would explain the contagious nature of yawning. When we see someone yawning, or even think of yawning, we yawn too. Contagious yawning, called by ethologists behavioral imitation and by neurologists echokinesis, would be a form of communication and one that could reinforce group behavior as well as our capacity for empathy [13,14]. Empathy is gradually built up as we grow and some never experience it. Autistic children and adults, whose capacity to feel empathy is frequently impaired, are immune to contagious yawning [15,16]. The Dutch researcher Wolter Seuntjens sees yawning as a subconscious enticement to sex. However, he and his co-workers admit that they are unable to explain how we can decipher when a yawn is produced by boredom and sleepiness or by an invitation to sex [17].
According to the obstetrician Richard Roberts, yawning ex utero would simply be a useless vestige of our fetal past [18]. Early fetuses would yawn (and hiccup) during the first trimester of pregnancy to assure patent airway development and consequently lung development by preventing the formation of tracheal and bronchial webs but would then continue to yawn and hiccup at later stages before and after birth without these having any function at all.
The list could continue. As Provine notes, however, "Those expecting a single, definitive function may probably be frustrated by the answer - it probably has many" [1]
Why Do Fetuses Yawn?
The most probable functions of fetal yawning will be analyzed below, after first describing when fetuses start yawning and how they yawn. Since the pioneering work of de Vries and collaborators, it has been discovered that fetuses yawn from the early fetal stages, starting between 10 and 12 weeks [19]. Some date the fi rst yawns even earlier, at the end of the embryonic phase. However, prior to 12 weeks, one can note just a quick (1-2 s) wide opening of the mouth followed by an equally quick (1 s) closure similar to "yawn" in fishes. One wonders if this quick wide opening can be considered a yawn or perhaps a pre-yawn or instead a simple wide opening of the mouth. Yawns can be observed till the end of pregnancy [19, 20]. In interpreting fetal yawns one always has to take into account the shape and characteristics of the fetal thorax
Though all can recognize fetal yawns just as they can recognize a neonatal or an adult one and distinguish a yawn for other kinds of mouth openings, a thorough definition of fetal yawning taking into account all its components has not yet been given.
de Vries describes yawns as "a prolonged wide-opening of jaws, followed by quick closure, often with retroflexion of the head and sometimes elevation of the arms." Additionally, de Vries points out that yawns are usually non-repetitive [ 21].
Provine, expanding on the latter point, added a more complex (postnatal) definition based on ethology. "The yawn is highly stereotyped, but not invariant in duration and form. It is an excellent example of the instinctive "fixed action pattern" of classical animal behaviour study, or ethology. It is not a reflex, a short duration, rapid, proportional response to a simple stimulus. But once started a yawn progresses with the inevitability of a sneeze. The yawn runs its course for about six seconds on average, but its duration can range from about three and a half seconds to much longer than average. There are no half- yawns, an example of the "typical intensity" of fixed action patterns and a reason why you cannot stifle a yawn. Yawns come in bouts, with a high variable inter-yawn interval of around 68 seconds. There is no relation between yawn frequency and duration; producers of short or long yawns do not compensate by yawning more or less often" [7].
Recently Asim Kurjak, an obstetrician and an expert in 3- and 4D ultrasound, defined a fetal yawn as, "A paroxysmic cycle characterized by a standard cascade of movements over a 5- to 10-second period. The fetal mouth, previously closed opens widely for 4-6 sec with simultaneous retraction of the tongue, followed by a quick closure and usually combined with retroflexion of the head and sometimes elevation of the arms (pandiculation). This harmonious sequence is markedly different from a brief swallowing episode." And he then adds, quoting the work of others, "Using a color Doppler technique, it is possible to observe the flow of amniotic fluid through the fetal mouth, oropharynx, pharynx and trachea to the lungs" [22].
Beyond the very initial stages, fetuses do not stretch their arms or pandiculate when yawning. However, the most important and widespread misconception is that yawns ultimately fill the lungs with swallowed amniotic fluid. The question of whether the amniotic fluid contributes to lung development has been hotly debated in the past but was proved wrong by Jost and Policard in 1948 [23]. However, despite widespread evidence to the contrary, many still claim that the amniotic fluid is swallowed into the lungs and by doing this plays an essential role in their growth.
As to other hypotheses, clearly fetuses do not socialize, imitate, communicate and feel empathy and boredom or are prone to sexiness. All these feelings and behaviors only pertain to life after birth.
The state change hypothesis, though plausible, could apply to the last few weeks of pregnancy only, but fetuses start yawning long before that. On the other hand, Richard Robert's theory, claiming that yawns (and hiccups) help in keeping our airways patent during fetal life, seems the most apt to explain fetal yawns [18]. As he says, "These reflexes may be necessary for the normal development of the airway passages during organogenesis in the first trimester, helping to prevent bronchial and tracheal webs. Bronchial webs may lead to focal adenomatous malformation of the lung. Should a tracheal web occur, the evolutionary fitness for that individual is 0, since the organism would die at birth. Both reflexes would serve to dislodge potential webs from formation through hydraulic pressure variation… Hence, the reason why we yawn and hiccup is simply because we had to do it in the fi rst trimester to assure patent airway development, and postnatally the reflexes just keep going" [18]. Even this hypothesis, however, needs further expanding and clarification.
Yawns enlarge all three dimensions of the rib cage and stretch and push down the diaphragm greatly in a different way from that occurring during ordinary fetal breathing motions. Fetal breathing motions do not enlarge the rib cage in the same way. Fetuses when yawning also greatly enlarge the larynx and the trachea and stretch the head backward.
Fetal yawns initially occur predominantly, but far from exclusively, within epochs when general movements surface, and yawns do not intermingle with fetal breathing movements. Fetuses generally stop moving, yawn once, and then resume moving. Consecutive yawns are not the rule, but they do occur. General movements produce notable distortions of the compliant rib cage, with consequent squeezing of the lungs. Taking a good yawn could help the lungs to go back into shape while redistributing lung fluid in all its compartments. The immature lung contains relatively few elastin and collagen fibers and has little elastic recoil [24].
Besides stretching the diaphragm and enlarging the rib cage in a unique way, the stretching of the spinal column and neck during yawns could possibly be important for tracheal expansion and growth.
The function of yawns, however, may not be limited to the first trimester of pregnancy alone. Mid-pregnancy periods of rest are short, lasting on average 6-8 min. With advancing gestation, rest cycles become more prolonged, thus making rest and activity cycles clearly defi ned by 29 weeks [25]. Yawns become increasingly complex acts.
At 27-30 weeks, yawns also emerge just before and after periods of rest which by then begin to take on the characteristics of Quiet Sleep. During Quiet Sleep, sustained breathing motions are absent and only a shallow form of breathing emerges; muscular tone is greatly diminished and low; and consequently, the rib cage (with its intercostal muscles), the trachea, and the lungs tend to collapse. Having few good yawns before and after Quiet Sleep could rearrange the system and prevent tracheal and pulmonary atelectasis defined as the obstruction and collapse of the trachea and of the lungs. Congenital or inborn pulmonary atelectasis is more common in premature and weak infants, but it can affect all infants. Eliot Katz of the Pulmonary Department of the Harvard Medical School says a propos of preterm infants that sighs and yawns "Are important to redistribute surfactant and maintain ventilation perfusion matching. A loss in lung volume predisposing them to the development of peripheral airway closure is particularly relevant to young infants. Lung volume falls if respiration ceases as during apnoeas, which is one of the reasons of the high respiratory rate of infants (term and preterm). One of the main functions of sighs in preterm infants is to reverse falls in lung volume caused by apnoeas" [26,28].
The problem of tracheal and lung collapse with the possible formation of atelectasis is well known to anesthesiologists and surgeons, especially those involved in cardiac and abdominal surgery. In infants, given their highly deformable chest wall, the problem is particularly severe and acute. The usefulness of deep sighs and yawns could, however, extend to later stages in life.
After surgery, even adult patients are encouraged to take deep breaths and yawn (as well as to cough) [29,30].
However, as Provine says, yawns may have more than one function [1]. Yawns preceding and following sleep may also fulfill the function hypothesized by Provine, being inducers or precipitators of an emerging state.
Additionally, in the late stages of pregnancy, yawns may have a preparatory communicative function. After birth, yawns start to belong increasingly to the category of facial expressions. Infants and young children are intent in fighting for their survival and trying to have their basic needs met, including sleep, a predominant feature of their lives. Yawns clustering before epochs of rest may be anticipatory in the sense of preparing the future neonate to communicate albeit not consciously the need for sleep.
The contagious and imitative component of yawning does not appear in them before 3-4 years of age. Possibly, no matter how exhausted and sleepy their caregivers may be, young children still need to be fed and put to sleep, signaling the latter need with one or more yawns. Some could say that infants are selfish creatures, but being utterly dependent on their caregivers for survival as they are, they cannot take into account the fatigue of those looking after them and providing for their essential demands. If they did so, our species would have long been extinct.
Au cours des derniers stades de la gestation, les fonctions fœtales subissent un changement et un développement accrus, préparant le fœtus à la transition vers son environnement postnatal. Cette maturation rapide est observée pour la respiration, la déglutition, les fonctions sensorielles, le sommeil et de nombreux autres processus, avec des changements de comportement correspondants.
De 35 à 40 semaines de gestation, les fœtus sont capables de vivre ex-utero sans aide, mais il est de plus en plus considéré que même les nourrissons nés entre 35 et 36 semaines peuvent en pâtir à long terme.
Ce livre, qui complète le volume précédent de l'auteur sur le développement des mouvements fœtaux normaux pendant les 25 premières semaines de gestation, discute en détail l'ensemble des phénomènes comportementaux observés pendant les 15 dernières semaines de gestation, avec une analyse attentive de leurs relations mutuelles.