Pregnancies affected by gestational diabetes (GDM) commonly result in large-for-gestational-age (LGA) infants; these infants have an increased risk of developing cardiometabolic complications compared to appropriate-for-gestational-age (AGA) infants. The mechanisms responsible are unclear but GDM/LGA is associated with altered placental development/function. We have recently reported altered levels of extracellular vesicle (EV) encapsulated miRNAs, including miR-375 (a pancreatic-specific miRNA) in maternal serum prior to the onset of LGA. We propose that the EVs containing miR-375 are produced by maternal pancreas, and that increased miR-375 in maternal circulation contributes to LGA by influencing placental development/function. Human placental tissue was collected from GDM pregnancies that delivered AGA (n=14) or LGA infants (n=10). Levels of mature miR-375 and primary transcript (pri-miR-375) were measured by QPCR. Mature miR-375 was increased in GDM-LGA (4.74-fold; p<0. 01) compared to GDM AGA placentae. Mature miR-375, but not pri-miR-375, was detected in human placenta suggesting that miR-375 is not produced in the placenta but instead is transported, potentially via EVs in maternal circulation. Intact human pancreatic islets (20,000 IEQ/patient) were obtained through the Integrated Islet Distribution Program (IIDP) from female donors of reproductive age. Islets were cultured in EV-depleted media containing 5.5mM (normoglycemia) or 7mM (mild hyperglycaemia) glucose for 3 days. Islet purity and viability were confirmed using dithizone incorporation and trypan blue exclusion, respectively. Media was collected at 24-hour intervals, pooled from all time points, concentrated and EVs were isolated by size exclusion chromatography. Confirmation of the presence of EVs was confirmed by electron microscopy (typical cup-shape morphology of EVs), nanoparticle tracking analysis (NTA; mean size of 83.5-163.2nm; concentration of 1.28×109-1.82×1010 particles/ml), Western blotting (EV-enriched proteins). QPCR confirmed that mature miR-375 was present in islet-derived EVs and revealed that levels were altered following culture in 7mM glucose compared to 5.5mM. Islet-derived EVs were labelled with maleimide-488 and uptake into explants of normal human term placenta was confirmed using fluorescent microscopy=3). miR-375 was overexpressed in normal human placental explants (by 30-fold, p<0. 05; n=6) using specific mimics (100nM for 72 hours) and TMT mass spectrometry was performed to assess the impact of miR-375 overexpression on the placental proteome. Functional enrichment analysis (FEA) was performed on differentially expressed proteins (DEP; P<0. 05; -0.41≥log2foldchange≥0.58) using over representation analysis and Ingenuity Pathway Analysis. This revealed that DEGs were significantly enriched in pathways associated with placental growth, mitochondrial function and glucose metabolism. Our data demonstrates that miR-375 is increased in the placenta in GDM/LGA and that this influences placental development/function. miR-375 does not appear to be produced in the placenta but instead, is likely released in EVs from maternal pancreas under conditions of hyperglycaemia and transported to the placenta, via maternal circulation. This provides insight into the potential mechanisms contributing to LGA in pregnancies complicated by GDM. Presentation: No date and time listed