The objective of this study was to characterise the changes in the exosomal miRNA concentrations circulating in the maternal plasma between mothers delivering term and preterm neonates, across gestation using a longitudinal study design. A retrospective stratified study design was used to characterize the miRNA content in exosomes present in maternal plasma of term (n=20 per time point) and preterm birth (PTB) (n=10 per time point) across gestation (i.e. first, second and third trimester). Overall design: miRNAs were profiled from exosomes using next generation seqeuencing (Illumina NextSeq 500 platform).