Age at menarche and age-adjusted anti-Müllerian hormone level among women of childbearing age in China.

BACKGROUND: Trends toward earlier age at menarche, the starting point in women’s reproductive lifespan, have been observed globally. Whether an earlier age at menarche influences Anti-Müllerian hormone (AMH), a clinical indicator of ovarian reserve, remains unclear due to a lack of community-based data. MATERIALS AND METHODS: This nationwide cross-sectional survey was carried out in China’s 15 provinces from May 2019 to April 2021, utilizing a multistage stratified sampling method to ensure sample representativeness and containing a total of 8 278 women aged 21–49 years. Self-reported age at menarche acts as exposure. Participants were categorized as age at menarche < 14 years group (N = 4 022) and age at menarche ≥ 14 years group (N = 4 256). AMH and AMH subgroups act as primary outcomes. RESULTS: A total of 8 278 participants were enrolled in this study. Mean (SD) age at menarche of the participants was 13.74 (1.58) years. Age at menarche decreased nearly 1 year from 14.31 years in women aged 45–49 to 13.38 years in women aged 21–24. For every one-year increase in age at menarche, AMH increases by 0.04 ng/ml. Compared with women with age at menarche < 14 years, women with age at menarche ≥ 14 years tend to have higher AMH level no matter in Middle AMH Group (OR, 1.28; 95%CI: 1.07–1.54) or in High AMH Group (OR, 1.43; 95%CI: 1.14–1.80) compared with Low AMH group, especially in women aged 25–29 years and 35–39 years. Stratified analysis showed associations between age at menarche and AMH in women with normal BMI group of 18.5–23.9 kg/m2, regular menstrual cycles, menstrual cycle length of 21–34 days, without polycystic ovary syndrome, infertility, or thyroid-stimulating hormone > 4.0 µIU/ml. CONCLUSIONS: Our results support the opinion that women with early age at menarche in a community-based population have lower AMH level. Periodic AMH monitoring are necessary in children/adolescents with an early age at menarche. For individuals with early age at menarche, they should consider the optimal timing for childbearing.