Baseline characters of participants
The baseline characteristics of the participants are summarized in Table 1. Throughout the study (Figure 1B), 322 infants developed symptoms or signs of respiratory distress in the monitoring room. All of them underwent LUS, and clinical data were collected. Twelve of these infants were excluded according to the stated criteria (4 with complex malformation or congenital lung diseases, 3 were transferred to another hospital, and 5 did not have qualified LUS images). A total of 310 infants were enrolled, and their LUS images were obtained at one of following times—-(67, 85, 92, 37, 29 infants with LUS obtained at at 0.5 h, 1 h, 2 h, 4 h, 6 h after birth, respectively). After the three-day follow-up, 236 infants were confirmed to be healthy, and 74 were admitted to the NICU due to pulmonary issues, including RDS (28/74), TTN (31/74), pneumonia (6/74) and MAS (6/74). The GA range was 34w+0d to 41w+5d, and the birth weight range was 1990 g to 4520 g. Most NICU and healthy infants were scanned at second 2 hour after birth. Infants admitted to the NICU were more likely to have a higher respiratory rate (65 (87.8%) vs 57 (24.2%), p<0.01) and a higher incidence of lower TcSO2 (below 95% for more than 3 mins, 23 (31.1%) vs 18 (7.6%), p<0.01) than the healthy infants.