a, Flow chart of the overall approach. GW, gestational week. b, Principal component (PC) analysis plots of samples coloured by their age groups. c, Hierarchical clustering of samples based on proteins with differential abundance. d, GSEA for individual age groups. NES, normalized enrichment score; KEGG, Kyoto Encyclopedia of Genes and Genomes; PID, Pathway Interaction Database; reg, regulatory; GPCR, G-protein-coupled receptor. Nominal P values were adjusted (adj) by the Benjamini–Hochberg method.