Funding: the study was supported by the RSF grant [22-15-00363 “Epigenetic and biochemical aspects of abnormal pregnancy in disturbances of the trophoblast invasive properties: from early diagnosis to prevention of maternal and perinatal morbidity”].

Author contribution: Gusar VA, Timofeeva AV — study concept; Fedorov IS — statistical analysis, graphic design; Gusar VA, Tarasova AM — research procedure (western blotting); Sukhova YuV, Ivanets TYu — providing the clinical basis, assessment of hormones; Gusar VA — data analysis/interpretation, manuscript writing; Timofeeva AV — editing.

Compliance with ethical standards: the study was approved by the Ethics Committee of the Kulakov National Medical Research Center for Obstetrics, Gynecology and Perinatology (protocol № 13 dated 12 October 2015); the informed consent was obtained from all the patients enrolled.