Fig. 2

The flowchart of the selection process of the study population. Pregnant women who met the following criteria were enrolled in the study: (1) singleton pregnancy; (2) those with complete medical information who had undergone maternity examination and subsequent delivery in our hospital; (3) fetuses with no known congenital malformation or chromosomal abnormality; (4) those with no diabetes before pregnancy; and (5) those who had not been prescribed steroids before delivery. Finally, a total of 210 singleton pregnant women with 210 fetal lung ultrasound images were enrolled in our study and randomly divided into the training set and test set at a ratio of approximately 8:2. It is worth noting that we kept the same proportion of NRM and normal in both sets. The training set contains 167 images, of which 40 are NRM and 127 are normal. The test set contains 43 images, of which 11 are NRM and 32 are normal