Age at menarche has declined in many populations, but whether earlier menarche is related to ovarian reserve markers and biological aging in young adulthood remains unclear. In this cross-sectional study, we compared 82 women with early menarche (<12 years) and 92 women with normal menarche (12-13.5 years), all aged 18-25 years, from Anhui Province, China. Serum anti-Müllerian hormone (AMH), follicle-stimulating hormone (FSH), luteinizing hormone and estradiol (E2) were measured; antral follicle count (AFC) and ovarian volume were assessed by transabdominal ultrasound; and biological age was estimated using the Klemera-Doubal method (KDM-BA) and Phenotypic Age (PhenoAge). After adjustment for potential confounders, early menarche was associated with lower AMH (-15.5%, 95% CI: -26.8% to -2.4%) and AFC (-6.2%, 95% CI: -11.4% to -0.8%), higher FSH (22.1%, 95% CI: 5.5% to 41.3%) and E2 (25.7%, 95% CI: 6.5% to 48.3%), and greater KDM-BA acceleration (0.75 years, 95% CI: 0.04 to 1.46), but not with PhenoAge acceleration. These associations were modest: menarche group explained only 1.4%-4.1% of the variance in these outcomes. Early menarche is associated with small differences in ovarian reserve markers and biological age in young women; however, on its own it is unlikely to indicate a clinically meaningful reduction in reproductive potential.
