Circulating Anti‐Müllerian Hormone Reflects the Medium Antral Follicle Pool Following Histological Redefinition of Follicle Size in the Common Marmoset ( Callithrix jacchus )

Background Anti‐Müllerian hormone is widely used as a marker of ovarian reserve, but its stage‐specific follicular origin remains unclear in the common marmoset ( Callithrix jacchus ). Methods Follicle diameters were reassessed histologically, and plasma anti‐Müllerian hormone concentrations were measured using an ultrasensitive enzyme‐linked immunosorbent assay and analyzed in relation to stage‐specific follicle populations across 57 females of different ages. Age‐related differences in plasma anti‐Müllerian hormone were also evaluated. Results Histological measurements showed that antral follicles were smaller than previously reported. Plasma anti‐Müllerian hormone declined with age ( R 2 = 0.51, p < 0.001) and was most strongly associated with bilateral medium antral follicle count per animal ( R 2 = 0.64, p = 0.0002), whereas associations with preantral stages were minimal. Immunostaining localized anti‐Müllerian hormone mainly to granulosa cells of antral follicles. Conclusions Circulating anti‐Müllerian hormone in the common marmoset primarily reflects the developing antral follicle pool and may serve as a stage‐specific biomarker of ovarian function.