The aim of the study is to provide a rationale for the morphological diagnostic criteria of respiratory distress syndrome (RDS) and acute respiratory distress syndrome of the newborn (ARDSN) in extremely preterm newborn infants.Materials and methods. Autopsy protocols of 31 newborns were studied. The average gestational age of children was 28.9±5.3 weeks, body weight at birth was 1404±945 grams. Fifty eight percent of newborns in the sample had extremely low body weight (ELBW). At birth, all

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... borns were found to have severe asphyxia, and the median score on the Apgar scale at the 1st minute of life was 3 [2; 5] points. In all cases there was an unfavorable course of the disease. The median life span was 72 [22; 181] hours.The results of the study. The study revealed two variants of hyaline membrane formation in preterm newborns with acute respiratory failure. Hyaline membranes in the lungs were found in 93.5% of newborns, in 51.6% of cases there was ARDSN due to the primary surfactant deficiency, in 41.9% of children ARDS was due to immature lung being exposed to various direct and indirect damaging factors. In all cases a distinct morphological pattern in newborns with the hyaline membranes was identified: immaturity and antenatal damage to air-blood barrier, pneumonia, microaspiration, ischemia of the lungs.Conclusion. Acute respiratory distress syndrome is typical for 41.9% of extremely preterm infants, its development is favored by exposure of immature lungs to direct (congenital pneumonia, amniotic fluid aspiration) and indirect (severe perinatal hypoxia with ischemia, shock, hemorrhagic syndrome) damaging factors. Morphological signs of ARDS were most often found in newborns with congenital pneumonia, asphyxia, neonatal aspiration of amniotic fluid.