(A) Measurement of lung gas volume at 40 cmH₂O on the pressure volume curve (PV40) was performed on fetal lungs immediately following euthanasia. Preterm samples had the lowest PV40 and term samples the highest, with substantial variation among antenatal corticosteroid treated animals. Male and female fetuses are separately indicated. (B) Statistical enrichment of gene sets from diverse single-cell data sets (n > 2,000) for lung and amniotic fluid transcripts that are positively correlated with PV40, across the collection of rhesus samples (2 outlier animals removed). Cell type signatures associated with endothelial cells, lung cells, immune, and cell type signatures associated with endothelial cells, lung cells, immune, and other annotated cell types are highlighted, along with significant enrichment results (Z score > 2, Fisher’s exact P < 0.05 [FDR corrected]) in either or both lungs and amniotic fluid. (C) Data plotted as in B, comparing statistically enriched single-cell signatures from brain and amniotic fluid samples. (D) RNA maturity scoring algorithm design. Differentially expressed genes for term versus preterm control animals are calculated (see Methods) and selected for PCA of term and preterm samples to capture the loadings for PC1 to compute scores for all samples using the PCATools predict function. (E) In silico maturity scores from each fetus lung, brain, or amniotic fluid sample are displayed according to treatment group using either the scoring schema from that same tissue (left 3 plots) or for amniotic fluid scored based on the lung scoring schema for lung PC1 loading genes. Data on A and E are presented as individual values, with box representing the median and the 25th and 75th percentile and whiskers extending to ± 1.5 IQR. n = 47 animals for lung, 35 animals for amniotic fluid, and 46 animals for hippocampus.