THIN ENDOMETRIUM AND IMPLANTATION FAILURE IN ART/IVF: DIAGNOSTIC CRITERIA, ENDOMETRIAL RECEPTIVITY MARKERS, AND CONTEMPORARY TREATMENT STRATEGIES

Abstract

Background. Uterine-factor infertility, including thin endometrium and impaired endometrial receptivity, remains a major contributor to repeated implantation failure in ART/IVF. The absence of a universally accepted thickness threshold and the lack of a broadly accurate, accessible receptivity test complicate clinical decision-making.
Objective. To summarize diagnostic criteria for thin endometrium, review ultrasound and molecular markers of receptivity, and appraise evidence for conventional and emerging therapeutic options in women with reproductive failure.
Materials and Methods. A narrative review of Russian and international literature addressing endometrial thickness and pattern (M-echo, trilaminar morphology and classification), uterine/subendometrial perfusion, chronic endometritis, molecular markers (LIF, VEGF, integrins, pinopodes), and treatment strategies (estrogen supplementation, vasoactive agents, physical modalities, endometrial injury/scratching, intrauterine G-CSF, PRP, and cell-based therapies).
Results. Most studies report reduced pregnancy rates when endometrial thickness is <7 mm; however, successful implantation and live birth have been documented at lower thickness values when morphology and receptivity are favorable. Key etiologic factors include repeated intrauterine procedures, chronic inflammation, vascular/hemodynamic impairment, and hormonal disturbances. Regenerative and angiogenesis-oriented approaches (PRP, G-CSF) appear promising, while evidence for ERA-guided personalized transfer remains controversial.
Conclusion. Thin endometrium is a multifactorial condition requiring integrated assessment (morphology, inflammation, perfusion, and receptivity markers) and individualized management. High-quality RCTs using harmonized definitions and clinically meaningful endpoints (live birth) are needed to establish optimal care pathways.

Key words: thin endometrium; endometrial receptivity; window of implantation; recurrent implantation failure; in vitro fertilization; uterine artery Doppler; platelet-rich plasma.