Lung ultrasound
We performed beside LU at birth, at three days, and weekly thereafter until 36 weeks’ PMA, and we calculated LU score as previously described in neonatal patients 7 by adding the score (0-3) obtained in three areas of the thorax defined by the anterior axillary line, the posterior axillary line and the mammary line (upper anterior, lower anterior and lateral), with a total range of 0 to 18.
We used a portable ultrasound machine (Sonoscape Medical Corp., Shenzhen, China) with a high-frequency linear 8-15 MHz probe, holding the probe perpendicular to the ribs. All LU were performed by the same neonatologist, and were recorded anonymously.