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CONTEXT: During pregnancy, maternal insulin sensitivity decreases, supporting transfer of nutrients to the fetus; when excessive, this can lead to gestational diabetes mellitus. The physiological decline in insulin sensitivity is likely caused by placental factors; however, the identity of these placental factors remains unclear.OBJECTIVE: To identify placental microRNAs (miRNAs) associated with maternal insulin sensitivity during pregnancy.DESIGN: A prospective pregnancy cohort study called Genetics of Glucose regulation in Gestation and Growth. We assessed insulin sensitivity using the Matsuda index during the second trimester of pregnancy, and microtranscriptome expression in placental samples collected at delivery. We accounted for confounders including maternal age, fetal sex, gestational age at delivery, gravidity and maternal body mass index, and surrogate variables, capturing sampling and technical variability.SETTING: Centre Hospitalier Universitaire de Sherbrooke, Canada.PARTICIPANTS: A total of 434 pregnancies were included. The mean (SD) maternal age was 28.6 (4.4) years; Matsuda index, 7.7 (4.9); and gestational age at delivery, 39.4 (1.4) weeks.MAIN OUTCOME MEASURE(S): Placental miRNAs expression (n = 952 miRNAs).RESULTS: We identified 18 placental miRNAs negatively and 1 miRNA positively correlated with Matsuda index (FDR p < 0.05). Gene ontology and tissue expression analysis of the genes targeted by the identified placental miRNAs suggest they may influence metabolic regulation, potentially acting as endocrine factors in skeletal muscle and adipose tissue and as paracrine factors within the placenta.CONCLUSIONS: We identified placental miRNAs that may act as endocrine and paracrine factors to modulate maternal insulin sensitivity during pregnancy.