Lower limit of normal of cross-sectional area of peripheral muscles and diaphragm measurements performed with ultrasound in full-term and preterm infants.

To stratify groups of infants by gestational age and identify the lower limit of normal (LLN) of the cross-sectional area of peripheral muscles as well as diaphragmatic excursion and thickness and parasternal activation during spontaneous respiration in full-term and preterm newborns. A cross-sectional study was conducted at a neonatal unit. Preterm newborns (PTNBs) with gestational age of 28 to 36 weeks and full-term newborns (NBs) with gestational age of 37 to 41 weeks, clinically and hemodynamically stable, breathing ambient air with no signs of respiratory distress were included.