[en] OBJECTIVES. The objective of this research was to increase our knowledge about human birth ethology with the aim to improve the scientific foundations of obstetric routines. MATERIAL AND METHODS. This paper presents data from 34 healthy term newborns that were immediately placed in skin contact on their mother's abdomens and recorded from the first instants after normal vaginal birth. RESULTS. The frame-by-frame analysis of the 34 newborns' first facial expressions, body and limb movements observed two patterns of behaviour. The 12 infants in Group A were initially immobile and hypotonic for between 7 and 65 seconds. Then, after a startle reaction, they began to cry and move normally in the same way as the 22 infants in Group B did since the first instants of their birth. Before their startle reaction, Group A infants had irregular heart rate, fast breathing movements, and progressively mottled skin. The main symptom of their behaviour was a neutral facial expression with wide open eyes. This is known in ethology as the immobile or freeze reaction. The two factors associated with this reaction were artificial rupture of the membranes (ARM) (p < 0.05) and rubbing to dry the infant (p < 0.01). CONCLUSION. The immobile or freeze reaction has never been described in the human newborn. This reaction occurs in response to the neuroception of a life threatening danger such as hypercapnia. It is a defence strategy under the control of the amygdala, the vagal nerve, the hippocampus and the serotonin neurons of the brainstem. Given that those neural structures are involved in the pathogenesis of the Sudden Infant Death Syndrome (SIDS), we propose that Group A infants could be at risk for early neonatal or first months SIDS. Further research is needed to study the physiology of those infants and to develop a follow up for SIDS prevention. In the present state of our study, we recommend 1. Avoiding ARM, 2. Assessing the three vital signs: respiration, heart rate and colour, and avoiding any stimulation before progressing down the ILCOR neonatal flow algorithm, 3. Drying of the newborn should only be done gently without rubbing. Reference: Rousseau P. Ethology of human birth. I. Freeze reaction in human newborns. (Abstr.) Book of Abstracts, 21st European Congress of Obstetrics and Gynaecology. Antwerpen - Belgium, 5 to 8 May 2010. In: Facts, Views & Vision in ObGyn. Special edition, p. 70.
