Fetal yawning assessed by 3D and 4D sonography

The capacity of four-dimensional sonography to evaluate complex facial expressions allows recognition of a common behavior, yawning. Although there has been remarkably little interest in yawning in research and medical practice, even though it is an everyday phenomenon, we submit an original interpretation on the basis of knowledge derived from phylogeny and ontogeny. As a flip-flop switch, the reciprocal interactions between sleepand wake-promoting brain regions allow the emergence of distinct states of arousal. By its ontogenical links with REM sleep, yawning appears as a behavior which procures an arousal reinforcement through the powerful stretch and the neuromuscular rewiring induced. Yawning indicates a harmonious progress in the development of both the brainstem and the peripheral neuromuscular function, testifying to the induction of an ultradian rhythm of vigilance. The lack of fetal yawn, frequently associated with lack of swallowing, associated or not with retrognathia, may be a key to predict a brainstem’s dysfunction after birth.