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SUMMARY Suggestions that rapid eye movement (REM) sleep is ontogenetically primitive and observations of the behaviour of premature infants led to an attempt to trace the development of sleep in human infants from the premature period to three months after the expected date of delivery. Three sleep states were established, Quiet Sleep, Active Sleep (REM sleep), and Transitional Sleep, for the categorization of each 20 second interval of sleep during lengthy electroence‐phalographic and polygraphic recordings. Criteria regarding observed movements, eye movements, respiratory pattern, heart rate, chin electromyogram, and the EEG were used for a visual analysis of the tracings, with the specification that only four of the six criteria had to be met for classification of a 20 second interval as one sleep state or another. A second analysis, by means of computer sorting, was more rigid in that each 20 second interval had to meet all three criteria regarding observed movement, respiratory pattern, and eye movements. The other criteria were omitted. The second stricter analysis yielded a greater percentage of intervals that could not be called Active or Quiet Sleep and were, therefore, classified as Transitional Sleep, especially below 35 weeks gestational age. This finding/supports the concept that the sleep states of the more premature infants are less well defined and that the simultaneous occurrence of all the necessary criteria, particularly in Active 5jileep, is rarer than at later ages. Both analyses showed that the amount of Quiet Sleep increases as the infant matures, from 10 per cent at 31–32 weeks gestational age to roughly 50 per cent at 3 months past term. Conversely, Active Sleep decreases with maturation, the exact amount depending on the method of categorization. When the records were analysed visually, Active Sleep was found to constitute 68 per cent of the total sleep at 33–34 weeks gestational age and diminished to 36 per cent at 3 months; with computer sorting the comparable figures were 45 per cent and 25 per cent. Nevertheless, the figures for premature infants at term and 3 months were similar to those for full‐term infants at the same ages. The ill‐defined nature of the Active Sleep state in the early gestational ages and its subsequent delineation and diminution in amount amplify previous characterizations of this sleep state as a neurophysiologically primitive state and predecessor of the later stage during which dreaming occurs. RÉSUMÉ EAtats de sommeil chez les prématurés On a suggéré que le sommeil avec mouvements rapides des yeux (REM) est primitif ontogénétiquement; ceci, ajoutéà des observations du comportement des prématurés, nous a amenéà tenter de tracer le développement du sommeil chez les nouveaux‐nés humains depuis la période prématurée jusqu'à trois mois après la date prévue de l'accouchement. Trois états de sommeil ont étéétablis: Sommeil Tranquille, Sommeil Actif (Sommeil REM), et Sommeil Transitoire; pour la caractérisation de chacun d'entre eux on a étudié des intervalles de 20...

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SUMMARY Both the age of the infant and the birthweight in relation to age are relevant factors in studying prenatal and neonatal physiology and in evaluating immediate and future clinical risks to the fetus and the newborn. Since the true age of the infant (the time‐span from conception) is not available, the first day of the last menstrual period is commonly used as the time reference. In many cases, however, there is doubt as to the accuracy of this reference day, necessitating other criteria to indicate the duration of fetal development or of the postmenstrual age of the newborn. The authors discuss the use of pre‐ and postnatal evaluations of the developmental changes in various organ systems‐by physical measurement, observation, physiological registrations and biochemical analysis ‐ for the estimation of the postmenstrual age. They use the following criteria: Does the observable phenomenon change suddenly from absent to present at a particular postmenstrual age? Does the phenomenon remain unaltered in sick children? Is the method relatively easy and reliable? Is the technique without risk for the fetus, the mother and the newborn? At present, a combination of parameters, serially measured, on the developing nervous system and the developmental changes of the skin seem to be most helpful in pre‐ and postnatal life, and the authors report that the optimal accuracy obtainable so far still has a range of plus or minus 2–3 weeks. The reasons for this wide range are discussed. RÉSUMÉ Estimation de & lcar;âge post‐menstruel: vue d'ensemble L'âge de l'enfant et le poids de naissance en fonction de l'âge sont tout deux des facteurs importants dans l'étude de la physiologie prénatale et néo‐natale, dans l'évaluation clinique des risques immédiats et futurs du foetus et du nouveau‐né. Puisque l'âge vrai de l'enfant (durée depuis la conception) ne peut être connu, le premier jour des derniéres régies est pris généralement comme référence. Dans de nombreux cas cependant, on peut douter de la précision de cette référence et d'autres critéres sont néces‐saires pour indiquer la durée du développement foetal ou l'âge post‐menstruel du nouveau‐né. Les auteurs discutent l'emploi de mesures pré et post‐natales de modifications lieés au développement au niveau de certains organes pour la détermination de l'âge post‐menstruel (par mesure physique, observations, enregistrement physiologique et analyse biochimique). lis utilisent les critéres suivants: Le phénoméne observé“passe‐t‐il de l'absence à la présence brusquement à un âge post‐menstruel particulier? Ce phénoméne persiste‐t‐il chez les enfants malades? La méthode est‐elle suffisamment facile et fidéle? La technique est‐elle sans risque pour le foetus, la mére et le nouveau‐né? A l'heure actuelle, une combinaison de paramétres, déterminés sur des séries, au niveau du développement du systéme nerveux et des modifications progressives de la peau semble être la plus utile durant la vie pré ou post‐natale; les auteurs précisent que la précision optimale atteinte jusqu'a ce jour ...