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Objective To comparatively analyze the human microRNAomes between normal pregnant and miscarriage deciduas by an in-depth sequencing of microRNA (miRNA); and to specifically examine miRNA-199b-5p and serum/glucocorticoid regulated kinase 1 ( SGK1 ) in vivo and in vitro for their possible roles in pregnancy maintenance. Design Samples of deciduas from 6–8-week spontaneous miscarriages and normal pregnant women were irrespectively collected and comparatively analyzed by miRNA sequencing. The miR-199b-5p and SGK1 expressions were validated in vivo and in vitro. Setting University research and clinical institutes. Patient(s) In this experimental study, samples of deciduas were obtained from October 2011 to April 2012 from 29 women with spontaneous miscarriages and 35 normal pregnant women (control group) who underwent pregnancy termination at 6–8 weeks at our university gynecology unit. Intervention(s) Endometrial biopsies, cell transfection, and production of an miR-199b-5p transgenic mouse model. Main Outcome Measure(s) In-depth sequencing of the miRNAome on human deciduas was performed for statistically significant differences in miRNA expression. Expression levels of SGK1 were detected by quantitative polymerase chain reaction and immunoblotting (Western blot) in vitro while miR-199b-5p is overexpressed or knockdown in miR-199b-5p transgenic mice. Result(s) Expression of the 1,921 known miRNAs was analyzed in the study. In aborted deciduas, 0.57% of the miRNAs were expressed abundantly (>10,000 transcripts per million) and represented 86.38% of all the miRNA reads. Six miRNAs were down-regulated (let-7a-5p, let-7f-5p, let-7g-5p, let-7e-5p, let-7d-5p, and miR-98), whereas miR-199b-5p was significantly up-regulated. Overexpression or knockdown of miR-199b-5p in HEK293T and Ishikawa cells decreased or increased SGK1 expression. Furthermore, overexpression of miR-199b-5p in human endometrial stromal cells or in transgenic mouse decreased SGK1 expression at the mRNA and protein levels, respectively. Conclusion(s) Among the miRNAomes, the abundant expression of the let-7 members was decreased in aborted samples, whereas miR-199b-5p expression was consistently increased. A significant inverse correlation was found between miR-199b-5p and SGK1 in vivo and in vitro. [ABSTRACT FROM AUTHOR]