Serial Ultrasound Assessment of Diaphragmatic Function in Term Neonates During the First 48 Hours of Life.

Background/Objectives: The early neonatal respiratory transition involves rapid changes in lung aeration and respiratory mechanics, but serial diaphragm-ultrasound trajectories in term neonates remain incompletely characterized. To describe bilateral diaphragmatic thickness, excursion, and diaphragmatic thickening fraction (DTF) during the first 48 h after birth. Methods: This prospective, single-center observational study analyzed 112 term neonates with complete ultrasound examinations at 1, 24, and 48 h of life. Bilateral thickness, excursion, DTF, and lung ultrasound score (LUS) were assessed during quiet spontaneous breathing. Serial comparisons used the Friedman test. No a priori sample-size calculation was reported. The analysis included all eligible neonates with complete serial data. Results: Right and left excursion increased from 5.65 ± 0.71 and 5.64 ± 0.69 mm at 1 h to 5.91 ± 0.58 and 5.91 ± 0.54 mm at 48 h, respectively (p = 0.024 and p = 0.033; Kendall's W = 0.033 and 0.031). These effect sizes were small. DTF remained stable, whereas LUS decreased from 7.01 ± 2.64 at 1 h to 0.09 ± 0.35 at 48 h (p < 0.001; Kendall's W = 0.885). Conclusions: In this single-center cohort, lung aeration changed substantially during the first 48 h, whereas diaphragm-ultrasound changes were small. These preliminary trajectories are descriptive and require standardized, multicenter validation before they can be used as reference values or guide clinical decisions.