Compliance with ethical standards: the study was approved by the Ethics Committee of Ural State Medical University (Protocol № 7 dated September 20, 2019). Informed consent was obtained from all study participants.

Acknowledgement: the authors thank Khayutin V, director of “Garmonia” Medical Center (Yekaterinburg), for letting them use its facilities for this research study. We thank to the Center for Precision Genome Editing and Genetic Technologies for Biomedicine (Moscow) for the genetic research methods.

Author contribution: Voroshilina ES organized the study, reviewed the literature, performed real-time PCR and statistical analysis, contributed to manuscript preparation; Zornikov DL reviewed the literature, conducted statistical analysis, contributed to manuscript preparation; Koposova OV reviewed the literature, performed molecular genetic assays; Islamidi DK analyzed medical histories, recruited patients, performed endometrial aspiration and pipelle biopsies, contributed to manuscript preparation; Ignatova KY conducted histological examinations; Abakumova EI reviewed medical histories, recruited patients, performed endometrial aspiration and pipelle biopsies; Kurbatova NV reviewed medical histories, recruited patients, performed endometrial aspiration and pipelle biopsies; Plotko EE organized the study, reviewed the literature, contributed to manuscript preparation.