Total RNA was isolated from the placental tissue using the Gene MATRIX Universal RNA Purification Kit (EurX, Gdańsk, Poland) and supplemented with TRI-reagent (phenol equilibrated, stabilized: chloroform: isoamyl alcohol 25:24:1) (AppliChem GmbH, Darmstadt, Germany) and β-mercaptoethanol (Acros Organics, New Jersey, USA). The procedure was conducted according to the manufacturer’s protocol. 3 mg of each sample were homogenized using gentleMACS Tubes (Miltenyi Biotec GmbH, Bergisch Gladbach, Germany) and gentleMACS Dissociator (Miltenyi Biotec GmbH, Bergisch Gladbach, Germany). Total RNA quantity and concentration were measured with Nanodrop 2000 spectrophotometer (Thermofisher Scientific, Massachusetts, USA) and stored at -86°C. The RNA quantity included in the study ranged between 1.9 to 2.0, and the median RNA concentration for samples was 1000 ng/μl.