Participants
This was a prospective diagnostic accuracy study that followed the STARD (Standards for the Reporting of Diagnostic Accuracy Studies) guidelines19. The study was conducted at a top-ranking obstetrics and gynecology hospital in China between 2019 and 2020. All included infants were delivered at our hospital and were transferred to a monitoring room for 6-hour monitoring before going back to their mothers (healthy infants) or admission to the NICU (infants with respiratory issues or other diseases). (Figure 1A) Infants who had respiratory symptoms, including anhelation, retractions, or transcutaneous oxygen saturation (TcSO2) constantly below 95%, were considered eligible for the study. Then, the infants were confirmed to be healthy or in need of respiratory support over a 3-day follow-up. The exclusion criteria were as follows: (1) chromosomal abnormalities or complex congenital malformations; (2) congenital lung diseases; (3) transfer to other hospitals so that they could not be followed up; and (4) no qualified LUS images or complete data.