Research question Can a novel ultrasound-based endometrial repair score (ERS-US) reliably reflect histological endometrial repair, correlate with reproductive outcomes and be used to determine whether umbilical cord mesenchymal stem cell-derived exosomes (UC-MSC-Exos) are non-inferior to umbilical cord mesenchymal stem cells (UC-MSCs) in a rat intrauterine adhesion (IUA) model? Design Eighty Sprague-Dawley rats were randomized into control, IUA, UC-MSCs and UC-MSC-Exos groups (n = 20 each). IUA was induced by mechanical curettage; 1 week later the injured groups received intrauterine phosphate-buffered saline, UC-MSCs or UC-MSC-Exos, with sham-operated controls. Each group comprised structural repair and fertility outcome cohorts (n = 10 each). ERS-US (five dimensions, 0–15) and a histology-based score (ERS-histo; four dimensions, 0–12) used quartile-based thresholds, scored independently by two blinded raters. Agreement used Spearman correlation and Bland–Altman analysis; non-inferiority was tested by two one-sided tests with prespecified margins (ERS-US score, Δ = 1.5; thickness, Δ = 0.05 mm). Results ERS-US correlated significantly with the ERS-histo (r = 0.8121, P < 0.0001), and thickness on ultrasonography correlated strongly with histological thickness (r = 0.9941, mean bias 0.0027 mm). ERS-US was positively associated with pregnancy occurrence (odds ratio 1.354, P = 0.0273), live embryo count (r = 0.7262) and embryo size (crown–rump length; r = 0.6789) (both P < 0.0001). Non-inferiority of UC-MSC-Exos to UC-MSCs was established for both end-points. Longitudinal follow-up showed a significant group-by-time interaction with treatment-driven recovery. Conclusions ERS-US reliably reflects histological repair and is positively correlated with reproductive outcomes. Both UC-MSCs and UC-MSC-Exos improved endometrial repair, and UC-MSC-Exos were non-inferior to UC-MSCs, supporting their feasibility as a cell-free alternative.
