The aim of the study was to demonstrate that preterm birth (PTB) is associated with altered C19MC microRNA expression profile in placental tissues. Gene expression of 15 placental specific microRNAs (miR‑512‑5p, miR‑515‑5p, miR‑516‑5p, miR‑517‑5p, miR‑518b, miR‑518f‑5p, miR‑519a, miR‑519d, miR‑519e‑5p, miR‑520a‑5p, miR‑520h, miR‑524‑5p, miR‑525‑5p, miR‑526a and miR‑526b‑5p) was compared between groups: 34 spontaneous PTB, 108 preterm prelabor rupture of membranes (PPROM) and 20 term in labor pregnancies. Correlation between variables including relative microRNA quantification in placental tissues and the gestational age at delivery, white blood cell (WBC) count at admission and serum levels of C‑reactive protein at admission in patients with PPROM and PTB was determined. Expression profile of microRNAs was different between PPROM and term in labor pregnancies, PTB and term in labor pregnancies, and between gestational age‑matched PPROM and PTB groups. When compared with term in labor pregnancies, while C19MC microRNAs showed a downregulation in PPROM pregnancies (miR‑525‑5p), in PTB pregnancies C19MC microRNAs were upregulated (miR‑515‑5p, miR‑516‑5p, miR‑518b, miR‑518f‑5p, miR‑519a, miR‑519e‑5p, miR‑520a‑5p, miR‑520h, and miR‑526b‑5p) or showed a trend to upregulation (miR‑519d and miR‑526a). In comparison to PTB pregnancies, the PPROM group demonstrated a significant portion of downregulated C19MC microRNAs (miR‑516‑5p, miR‑517‑5p, miR‑518b, miR‑518f‑5p, miR‑519a, miR‑519d, miR‑519e‑5p, miR‑520a‑5p, miR‑520h, miR‑525‑5p, miR‑526a and miR‑526b‑5p). In the group of PPROM pregnancies, a weak negative correlation between the gestational age at delivery and microRNA gene expression in placental tissue for all examined C19MC microRNAs was observed. PTB pregnancies showed a positive correlation (miR‑512‑5p, miR‑515‑5p, miR‑519e‑5p) or a trend to positive correlation (miR‑516‑5p, miR‑518b, miR‑520h) between particular C19MC microRNAs and maternal WBC count at admission. Our study demonstrates that upregulation of C19MC microRNAs is a characteristic phenomenon of PTB. PPROM pregnancies have a tendency to produce lower levels of miR‑525‑5p. All examined C19MC microRNAs displayed decreased expression with advancing gestational age in PPROM group.

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