MicroRNAs (miRs) are the class of short nucleotide sequences (21-27 nucleotides) RNA, non-coding protein synthesis. miRs are known as effective posttranscriptional negative regulators of gene expression with specific binding sites of targeted messenger RNA (mRNA) in the cytoplasm, providing translational repression or degradation of the target miR transcript. In this review we studied the role of miRNAs in the development of a physiological pregnancy and obstetric complications. The placenta is a unique organ which provides modulation of the immune system of the maternal organism during pregnancy including miRs which determine immunological tolerance of the body to the tissues of the fetus. Thus the "placental" miRs in maternal circulation may be the potential biomarker revealed at various obstetric pathology on the early stages before clinical manifestation of the diseases.