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

The China Fertility Survey of Married Women (CFSMW) program was carried out in China from May 2019 to April 2021, utilizing a multistage stratified sampling method to ensure sample representativeness. The selection process began with the identification of top 15 provinces and municipalities across mainland China’s southeast, southwest, central, and northeast regions, namely: Shanghai, Zhejiang, Fujian, Guangdong, Hainan, Sichuan, Guizhou, Yunnan, Liaoning, Beijing, Tianjin, Hebei, Shanxi, Henan, and Hubei. The 15 provinces/municipalities contain the major residential population from 30 provinces of the whole China. A multi-layer, stratified sampling method was performed from each province or municipality by city or district, town/township and village/street order and ultimately selected communities. Within each province, three counties or districts were chosen randomly according to their urbanization level and population size. Subsequently, two to four villages or residential communities were randomly selected from each county or district. The randomization method was described in detail in Yang’s study [ 36 ]. From each of these units, 100 married women meeting the eligibility criteria (aged 21–49 years and local residents for at least six months) were invited to join the study. Trained healthcare personnel conducted face-to-face interviews using a structured questionnaire to gather detailed sociodemographic and reproductive information. Venous blood samples were also obtained from each participant. Flow diagram of the women recruited in this study was showed in Fig.  1 . A total of 12 815 women aged 21–49 years, who were local residents for at least six months, provided informed consent, completed the survey, and submitted blood samples, were included in the study. Individuals, of whom 116 women were pregnant, 2 676 women missed AMH values, 384 women missed AFC values, 1 347 women missed AAM and 14 women aged 20 or had a history of ovarian surgery, were excluded. Fig. 1 Flow diagram of the women recruited in this study. Abbreviations: AMH, Anti-Müllerian hormone; AFC, antral follicle counts; AAM, age at menarche Flow diagram of the women recruited in this study. Abbreviations: AMH, Anti-Müllerian hormone; AFC, antral follicle counts; AAM, age at menarche A structured questionnaire included the following sections: (1) General background information; (2) Menstrual, marital and childbearing history. There were 17 questions in total, and full questionnaire details are provided in the Supplementary file 2. The questionnaire was performed by trained healthcare personnel through face-to-face interviews. Menstrual information was gathered. Participants were asked to self-report their AAM. According to the average AAM of 13.73 years, Participants were categorized as AAM<14 years group ( N  = 4022) and AAM ≥ 14 years group ( N  = 4 256) averagely. Participants with incomplete AAM data were excluded from the analysis. Blood samples were collected at random menstrual cycle days using separation gel coagulant tubes (4 mL) and allowed to clot at room temperature. Two hours post-collection, the samples were centrifuged (3000 g, 10 min, 4℃) to isolate serum, which was then aliquoted into cryovials and stored at -80℃ until analysis. Serum anti-Müllerian hormone (AMH) levels were measured with ultrasensitive two-site enzyme-linked immunosorbent assays (ELISA; Ansh Labs, Webster, TX)⁠ by certified technicians at the Reproductive Endocrinology Laboratory of Peking University Third Hospital. This laboratory is certified by the National Center for Clinical Laboratories for AMH measurement external quality assurance. Intra-assay coefficients of variation were below 8%, and the detection limit was 0.01 ng/mL. For modeling purposes, values reported below the detection limit (< 0.01 ng/mL) were imputed as 0.005 ng/mL. AMH was evaluated by its specific value and grouping. We have previously reported the fitted AMH percentile reference values [ 20 ]. According to 10% and 90% cutoff values per age, AMH was classified into three groups: Low AMH Group (AMH90% cutoff value). We included covariates in regression models as potential confounders based on a priori knowledge. All covariates were self-reported at enrollment, including: (1) sociodemographic factors: age; BMI; educational level (primary school and below, middle school, senior school, technical secondary school, junior college, master’s degree and above); employed (yes or no); annual household income per capita ( 50 000 RMB); household registration (rural citizens, urban citizens); current tobacco smoke exposure (yes or no); current alcohol consumption (yes or no); (2) menstrual status: AAM (< 14 years, ≥ 14 years); menstrual regularity (yes or no); dysmenorrhea (yes or no); menstrual cycle length ( 60 days); menstruation length (≤ 7 days, 8–10 days, > 10 days); (3) marriage and childbearing situation: gravidity (≥ 1, 0); age of first sexual intercourse ( 25 years). For continuous variables following a non-normal distribution, we calculated their median (IQR) and performed Mann-Whitney U test to identify the difference between groups. For categorical variables, we reported their numbers (percentages) and performed χ2 tests to identify differences between groups. Across 5-year age groups, AMH levels were compared the among different AAM groups. Ages were grouped age as 21–24 years ( n  = 312), 25–29 years ( n  = 1 162), 30–34 years ( n  = 1 850), 35–39 years ( n  = 1 785), 40–44 years ( n  = 1 657), and 45–49 years ( n  = 1 526). Multivariate logistic regression was conducted to evaluate associations between AAM and AMH. Cofounding factors adjusted for age, BMI, educational level, employed, annual household income per capita, household registration, current tobacco smoke exposure, current alcohol consumption, menstrual regularity, dysmenorrhea, age of first sexual intercourse, pregnancy, menstrual cycle length and menstruation length. Odd ratio (OR) represents the degree of correlation between AAM and AMH. P values were 2-sided, and P  < 0.05 was regarded as significant. Data were analyzed using SPSS statistical software version 29.0 (IBM).

The screening questionnaire was administered to a total of 12 815 women aged 21–49 years from May 2019 to April 2021, of whom 116 women were pregnant, 2 676 women missed AMH values, 384 women missed AFC values, 1 347 women missed AAM and 14 women aged 20, leaving 8 278 participants involves in this study. Participants were categorized as AAM<14 years group ( N  = 4 022) and AAM ≥ 14 years group ( N  = 4 256) averagely based on median AAM (Fig.  1 ). Due to improvements in nutritional conditions, there is a trend toward earlier menarche. To minimize the effect of age on AAM, we categorized participants per 5 years according to their ages. Baseline characteristics of 8 278 participants are shown in Table  1 . Overall, participants had a median (IQR) age of 37 (31, 43) years and median (IQR) BMI of 22.68 (20.70, 25.07) kg/m 2 . 727 (8.8%) of the participants were obese, 2 228 (26.9%) of the participants were overweight, and 454 (5.5%) of the participants were underweight. Among them, 3 074 (37.1%) of the participants had a master’s degree, 6 610 (79.9%) of the participants were employed, 4 359 (52.7%) of the participants were urban citizens. Most of the participants self-reported that they were free from tobacco (97.7%) and alcohol (84.4%) exposure. When it comes to menstrual status, marriage and childbearing situation, 1 792 (21.6%) of the participants had irregular menstrual cycles, among which 608 (7.3) of the participants had a shorter menstrual cycle length of below 21 days, 798 (9.6) of the participants had a longer menstrual cycle length of 35–60 days, 219 (2.6) of the participants had a longest menstrual cycle length of above 60 days, and 878 (10.6) of the participants had a menstruation length of 8–10 days, 103 (1.2) of the participants had a menstruation length of above 10 days. 3 184 (38.5%) of the participants self-reported a dysmenorrhea. Additionally, 5 241 (63.3%) of the participants encountered the first sexual intercourse aged 20–25 years, and 899 (10.9%) of the participants had not raised a child until surveyed (Table  1 ). Table 1 Baseline characteristics of participants enrolled in this study Variables Median (IQR)/ No. (%) Age, years 37 (31, 43) BMI, kg/m 2 22.68 (20.70, 25.07)  underweight (< 18.5) 454 (5.5)  normal (18.5–23.9) 4 827 (58.3)  Overweight (24.0-27.9) 2 228 (26.9)  Obese (≥ 28.0) 727 (8.8)  Missing 42 (0.5) AAM, years 14 (13, 15)  ≤ 11 334 (4.0)  12 1 468 (17.7)  13 2 220 (26.8)  14 2 012 (24.3)  15 1 093 (13.2)  ≥ 16 1 151 (13.9) Educational level, n (%)  primary school and below 748 (9.0)  Middle school 1 591 (19.2)  Senior school 588 (7.1)  Technical secondary school 604 (7.3)  Junior college 1 583 (19.1)  Master’s degree and above 3 074 (37.1) Missing 90 (1.1) Employed, n (%)  No 1 523 (18.4)  Yes 6 610 (79.9)  Missing 145 (1.8) Annual household income per capita (RMB), n (%)  50,000 1 994 (24.1)  Missing 88 (1.1) Household registration, n (%)  Rural citizens 3 919 (47.3)  Urban citizens 4 359 (52.7) Current tobacco smoke exposure, n (%)  No 8 085 (97.7)  Yes 142 (1.7)  Missing 51 (0.6) Current alcohol consumption, n (%)  No 6 990 (84.4)  Yes 987 (11.9)  Missing 301 (3.6) Menstrual regularity, n (%)  No 1 792 (21.6)  Yes 6 291 (76.0)  Missing 195 (2.4) Dysmenorrhea, n (%)  No 4 871 (58.8)  Yes 3 184 (38.5)  Missing 223 (2.7) Age of first sexual intercourse, years  25 2 009 (24.3)  Missing 208 (2.5) Gravidity  ≥ 1 7 379 (89.1)  0 899 (10.9) Menstrual cycle length (days)   60 219 (2.6)  Missing 250 (3.0) Menstruation length (days)  ≤ 7 7 048 (85.1)  8–10 878 (10.6)  >10 103 (1.2)  Missing 249 (3.0) Abbreviations: BMI Body mass index, AAM Age at menarche Baseline characteristics of participants enrolled in this study Abbreviations: BMI Body mass index, AAM Age at menarche Of all the 8 278 individuals, mean (SD) AAM of the participants was 13.74 (1.58) years. There was an increased trend for AAM in women aged from 21 to 24 years to 45–49 years. Mean (SD) AAM of the participants aged 21–24 years, 25–29 years, 30–34 years, 35–39 years, 40–44 years and 45–49 years were 13.38 (1.53) years, 13.43 (1.43) years, 13.43 (1.51) years, 13.64 (1.50) years, 13.94 (1.54) years, and 14.31 (1.71) years respectively. AAM decreased nearly 1 year from 14.31 years in women aged 45–49 to 13.38 years in women aged 21–24 (Fig.  2 A). Among women aged from 45 to 49 years to 21–24 years, the percentage of AAM ≥ 16 years decreased from 23.6% to 7.3%, and the percentage of AAM ≤ 11 years increased from 2.2% to 6.3% (Fig.  2 B; full estimates are shown in Supplementary Table 1). Fig. 2 AAM Changing Trends Among Different Age Groups. A AAM changing trends in different age subgroups; B AAM distribution characteristic in different age subgroups. Abbreviation: AAM, age at menarche AAM Changing Trends Among Different Age Groups. A AAM changing trends in different age subgroups; B AAM distribution characteristic in different age subgroups. Abbreviation: AAM, age at menarche Table  2 ; Fig.  3 shows the associations between AAM and AMH. Compared with earlier AAM (< 14 years), participants with late AAM (≥ 14 years) tend to possess higher AMH level among women aged 21–49 years, but significant difference only occurs in women aged 35–39 years (Mann-Whitney U test for comparison of AMH value, Z = -2.02, P  = 0.043; χ 2 tests for comparison of Percentage of AMH subgroups, χ 2  = 7.43, P  = 0.024; Table  2 ). Table 2 AMH evaluation among total population and different age subgroups Age subgroups AAM < 14 AAM ≥ 14 Z/χ 2 P N  = 4 049 N  = 4 241 AMH value (ng/ml)  21–24 years 4.32 (2.85, 6.90) 4.43 (3.05, 6.36) -0.38 0.701  25–29 years 3.89 (2.49, 6.32) 4.08 (2.52, 6.84) -1.09 0.277  30–34 years 3.02 (1.75, 4.91) 3.14 (1.80, 4.99) -0.84 0.403  35–39 years 1.91 (1.01, 3.21) 2.07 (1.13, 3.46) -2.02 0.043  40–44 years 0.84 (0.31, 1.78) 0.84 (0.32, 1.66) -0.08 0.940  45–49 years 0.14 (0.06, 0.48) 0.15 (0.06, 0.49) -0.56 0.574 Percentage of AMH subgroups, n (%) 21–24 1.73 0.421  Low AMH Group ( 90%AMH) 23/181(12.7) 10/122(8.5) 25–29 3.43 0.180  Low AMH Group ( 90%AMH) 74/662(11.2) 70/500(14.0) 30–34 0.83 0.661  Low AMH Group ( 90%AMH) 133/1049(12.7) 97/801(12.1) 35–39 7.43 0.024  Low AMH Group ( 90%AMH) 67/893(7.5) 89/892(10.0) 40–44 2.61 0.272  Low AMH Group ( 90%AMH) 56/698(8.0) 67/959(7.0) 45–49 0.06 0.969  Low AMH Group ( 90%AMH) 45/539(8.3) 79/987(8.0) Abbreviations: AMH Anti-Müllerian hormone, AAM Age at menarche AMH evaluation among total population and different age subgroups Low AMH Group ( 90%AMH) Low AMH Group ( 90%AMH) Low AMH Group ( 90%AMH) Low AMH Group ( 90%AMH) Low AMH Group ( 90%AMH) Low AMH Group ( 90%AMH) Abbreviations: AMH Anti-Müllerian hormone, AAM Age at menarche After adjusting for all the covariates listed in Table  1 , compared with women with AAM < 14 years group, women with AAM ≥ 14 years group tend to have higher AMH level no matter in Middle AMH Group (OR, 1.28; 95%CI: 1.07–1.53) or in High AMH Group (OR, 1.42; 95%CI: 1.13–1.80) compared with Low AMH group totally. When grouped by age, the significant difference only presented in women aged 25–29 years (Middle AMH Group: OR, 1.40; 95%CI, 0.86–2.29; High AMH Group: OR, 2.25; 95%CI, 1.22–4.14) and 35-39years (Middle AMH Group: OR, 1.53; 95%CI, 1.07–2.18; High AMH Group: OR, 1.92; 95%CI, 1.18–3.14). There is no significant association between AAM and AMH in women aged 21–24, 30–34, 40–44 and 45–49 years (Fig.  3 A; full estimates are shown in Supplementary Table 2). When AMH and AMH are included as continuous variables in multiple linear regression, the study found that for every one-year increase in AAM, AMH increases by 0.04 ng/ml at the same age (Fig.  3 B; full estimates are shown in Supplementary Table 3). Fig. 3 Multivariate analysis results for the association between AAM and AMH in total population and different age subgroups. A AAM and AMH as grouped variables for multivariate analysis; B AAM and AMH as continuous variables for multivariate analysis. Cofounding factors adjusted for age, BMI, educational level, employed, annual household income per capita, household registration, current tobacco smoke exposure, current alcohol consumption, menstrual regularity, dysmenorrhea, age of first sexual intercourse, gravidity, menstrual cycle length and menstruation length. Abbreviations: AMH, Anti-Müllerian hormone; AAM, age at menarch Multivariate analysis results for the association between AAM and AMH in total population and different age subgroups. A AAM and AMH as grouped variables for multivariate analysis; B AAM and AMH as continuous variables for multivariate analysis. Cofounding factors adjusted for age, BMI, educational level, employed, annual household income per capita, household registration, current tobacco smoke exposure, current alcohol consumption, menstrual regularity, dysmenorrhea, age of first sexual intercourse, gravidity, menstrual cycle length and menstruation length. Abbreviations: AMH, Anti-Müllerian hormone; AAM, age at menarch To explore the association between AMH and AAM among different BMI and menstrual subgroups, stratified analysis was performed according to BMI, menstrual regularity, or menstrual cycle length respectively. When grouped by BMI, stratified analysis showed compared with women with AAM < 14 years group, women with AAM ≥ 14 years group tend to have higher AMH level no matter in Middle AMH Group (Middle AMH Group: OR, 1.37; 95%CI, 1.08–1.73) or in High AMH Group (OR, 1.48; 95%CI, 1.10-2.00) compared with Low AMH group in normal BMI group of 18.5–23.9 kg/m 2 . In underweight (BMI<18.5 kg/m 2 ), overweight (BMI 24.0–27.9 kg/m 2 ), and obese (BMI ≥ 28.0 kg/m 2 ) groups, there was no significant association between AAM and AMH (Fig.  4 A; full estimates are shown in Supplementary Table 4). In women with regular menstrual cycles, compared with women with AAM < 14 years group, women with AAM ≥ 14 years group tend to have higher AMH level no matter in Middle AMH Group (Middle AMH Group: OR, 1.32; 95%CI, 1.07–1.62) or in High AMH Group (OR, 1.39; 95%CI, 1.05–1.82) compared with Low AMH group in women with regular menstrual cycles. In women with irregular menstrual cycles, there was no significant association between AAM and AMH (Fig.  4 B; full estimates are shown in Supplementary Table 4). When grouped by menstrual cycle length, compared with women with AAM < 14 years group, women with AAM ≥ 14 years group tend to have higher AMH level no matter in Middle AMH Group (Middle AMH Group: OR, 1.28; 95%CI, 1.05–1.57) or in High AMH Group (OR, 1.35; 95%CI, 1.03–1.77) compared with Low AMH group in women with normal menstrual cycle length of 21–34 days. In women with menstrual cycle length of  60 days, there weas no significant association between AAM and AMH (Fig.  4 C; full estimates are shown in Supplementary Table 4). Fig. 4 Association between AAM and AMH in different BMI ( A ), menstrual cycle length status ( B ), menstrual regularity ( C ), and in subfertility-related conditions PCOS ( D ), infertility ( E ), and elevated TSH level ( F ). Abbreviations: AMH, Anti-Müllerian hormone; AAM, age at menarche; BMI, body mass index; PCOS, polycystic ovary syndrome; TSH, thyroid-stimulating hormone. Cofounding factors adjusted for age, BMI, educational level, employed, annual household income per capita, household registration, current tobacco smoke exposure, current alcohol consumption, menstrual regularity, dysmenorrhea, age of first sexual intercourse, gravidity, menstrual cycle length and menstruation length Association between AAM and AMH in different BMI ( A ), menstrual cycle length status ( B ), menstrual regularity ( C ), and in subfertility-related conditions PCOS ( D ), infertility ( E ), and elevated TSH level ( F ). Abbreviations: AMH, Anti-Müllerian hormone; AAM, age at menarche; BMI, body mass index; PCOS, polycystic ovary syndrome; TSH, thyroid-stimulating hormone. Cofounding factors adjusted for age, BMI, educational level, employed, annual household income per capita, household registration, current tobacco smoke exposure, current alcohol consumption, menstrual regularity, dysmenorrhea, age of first sexual intercourse, gravidity, menstrual cycle length and menstruation length To explore the association between AMH and AAM in subfertility-related conditions, further research explored the relationship between AAM and AMH through stratified analysis. Overall, when women were not suffering from PCOS, infertility, and hypothyroidism (TSH>4.0 µIU/ml), compared with women with AAM < 14 years group, women with AAM ≥ 14 years group tend to have higher AMH level compared with Low AMH Group (Non PCOS: Middle AMH Group: OR, 1.31; 95%CI, 1.09–1.57; High AMH Group: OR, 1.39; 95%CI, 1.08–1.78; Non infertility: Middle AMH Group: OR, 1.26; 95%CI, 1.00-1.60; High AMH Group: OR, 1.48; 95%CI, 1.08–2.02; TSH ≤ 4.0 µIU/ml: Middle AMH Group: OR, 1.27; 95%CI, 1.06–1.53; High AMH Group: OR, 1.36; 95%CI, 1.07–1.73). When women were diagnosed as PCOS, infertility or hypothyroidism (TSH>4.0 µIU/ml), there was no significant difference between AAM and AMH (Fig.  4 D ~ F; full estimates are shown in Supplementary Table 5).

This CFSMW program of 8 278 participants in China explored the trend toward earlier AAM and found the positive association between AAM and AMH, especially among women aged 35–39 years, during which women with early AAM possess decreased ovarian reserve compared with peers of the same age. We also identify the critical point at which AAM influences AMH remarkably was 35–39 years. Particularly, we found this trend existed in women at a state of normal BMI of 18.5–23.9 kg/m 2 , regular menstrual cycle, normal menstrual cycle length of 21–34 days, and without PCOS, infertility, or hypothyroidism. Our research indicates that further researches should focus on reproductive health of all ages. Screening and periodic AMH monitoring are necessary in children/adolescents with an early AAM. Parents and guardians can help prevent early menarche by fostering healthy habits in children. For individuals with early AAM, they should be encouraged to consider the optimal timing for childbearing.

This CFSMW program of 8 278 participants conducted in China from May 2019 to April 2021 explored the trend toward earlier AAM and found that AAM decreased nearly 1 year from 14.31 years in women aged 45–49 to 13.36 years in women aged 21–24. For every one-year increase in AAM, AMH increases by 0.04 ng/ml at the same age. Compared with women with AAM < 14 years group, women with AAM ≥ 14 years group tend to have higher AMH level no matter in Middle AMH Group or in High AMH Group compared with Low AMH group, especially in women aged 35–39 years, at which women with early AAM possess decreased ovarian reserve at same age. This trend remained after adjusting cofounding factors. Furthermore, we explicit the critical point at which AAM influences AMH remarkably was 35–39 years. Particularly, we found this trend existed in women at a state of normal BMI of 18.5–23.9 kg/m 2 , regular menstrual cycle, normal menstrual cycle length of 21–34 days, and without PCOS, infertility, or hypothyroidism. Our findings of a secular trend toward earlier AAM in recent years are consistent with previous studies [ 6 , 15 , 35 , 37 – 40 ]. The mean AAM among Chinese women has declined by nearly one year from 14.31 years in women aged 45–49 to 13.36 years in women aged 20–24, a greater reduction compared with the 0.6-year decrease observed in American women born between 1 950-1 969 and 2 000–2 005 [ 15 ]. The difference in the rate of AAM decline may attribute to more rapid economic development and greater improvements in nutritional conditions in China during this period. Most importantly, our results support the opinion that there is a positive association between AAM and AMH, indicating that women with earlier AAM have lower AMH levels compared to their peers of the same age [ 31 , 41 ]. However, opposite results were obtained in a prospective study in the Philippines, owing to their highly youthful population aged, with a narrow age gap of 20–22 years [ 32 ]. A key strength of our study is its comprehensive coverage of a community-based female population across the entire reproductive age range, thereby addressing a gap in the current literature. We found the critical trans-period at which AAM influences AMH remarkably was 35–39 years, coinciding with the stage of rapidly decreased female fertility [ 42 – 45 ]. The underlying mechanism remains unclear. Formers studies suggested accelerated depletion of the ovarian follicle pool and accumulated mitochondrial DNA mutations aged over 35 years may partially explain the phenomenon [ 45 – 47 ]. Our study addresses a critical gap in the current literature by elucidating the impact of AMH and fertility beyond the age of 35. Many clinical indicators influence the level of AMH. For example, BMI negatively impacted AMH levels according to several studies [ 48 – 50 ]. To explore underlying mechanism, researchers established murine model with obesity, and these mice showed reduced fertility, which is related to an increase in mitochondrial potential and reactive oxygen species [ 51 ]. Infertility is a heterogeneous condition with diverse etiologies, including PCOS, premature ovarian insufficiency, and endometriosis. The condition of infertility itself can lead to alterations in AMH levels, which may be either elevated or decreased, thus confusing the function of AAM on AMH in physiological conditions [ 52 , 53 ]. PCOS is a common cause of infertility, affecting an estimated 5–20% of reproductive-aged women worldwide [ 36 ]. In patients with PCOS, we found that earlier AAM was associated with higher AMH level, exhibiting a trend opposite to that observed in the general population. This could be because community-based AMH values were used as the reference standard for grouping. Patients with PCOS inherently have higher AMH levels, the Low AMH group (Reference group) contained very few PCOS patients ( n = 9). To increase the sample size of the reference group, we stratified the patients with PCOS into tertiles based on their AMH level, and found that earlier AAM was associated with lower AMH level (Supplementary Table 6). The relationship between AMH and AAM requires further investigation with larger sample sizes in patients with PCOS. Since elevated AMH levels are typically associated with longer menstrual cycle length, which is a clinical character of PCOS, there is a potential interplay between PCOS and abnormal menstruation [ 54 ]. Additionally, in patients with hypothyroidism, there is an interaction between AMH and abnormally elevated TSH level, and this action maybe be mediated by higher fat mass [ 55 ]. To control above indicators, stratified analysis was performed to control the effect of AAM on AMH from these confounding states. The results demonstrated a stronger association between AAM and AMH levels in women with normal BMI of 18.5–23.9 kg/m 2 , regular menstrual cycle, normal menstrual cycle length of 21–34 days, and without PCOS, infertility, or hypothyroidism. This may be because abnormal institution may influence AMH level and follicle consumption, which coincided with former studies. Moreover, we excluded women with PCOS, infertility or thyroid dysfunction (TSH>4.0 µIU/ml), and observe the association between AAM and AMH among the remaining women. The trend coincides with former study, while the difference isn’t significant, probably owing sample size limitation (Supplementary Table 7). Furthermore, unhealthy lifestyle habits, such as smoking and alcohol consumption, may have an impact on AMH levels. For example, studies have shown that smokers have significantly lower AMH levels compared to non-smokers [ 56 , 57 ]. To control above indicators, stratified analysis was performed to control the effect of smoking and drinking on AMH (Supplementary Table 8). The results demonstrated a stronger association between AAM and AMH levels in women without smoking and drinking. The effect of earlier menarche on ovarian function may be associated with alterations in neuroendocrine pathways and metabolic status. Epidemiological studies suggest a link between PCOS and earlier menarche, both of which are characterized by dysregulation of the neuroendocrine pathways that control pulsatile gonadotropin-releasing hormone secretion, thus affecting gonadotropin release, particularly LH secretion. Genome-wide association studies have identified common genetic variants associated with AAM, particularly in genes related to the neuroendocrine axis (e.g., FSHB ) and obesity (e.g., FTO ), indicating that the impact of early menarche on ovarian function may be related to neuroendocrine pathway alterations and metabolic changes [ 58 ]. Earlier AAM may be accompanied by an accelerated depletion of the ovarian follicular pool, which manifests as a more rapid decline in AMH levels. Our findings suggest that an earlier AAM is associated with a decline in AMH levels and diminished ovarian reserve. Against the backdrop of declining fertility and the social trend of delayed marriage and childbearing, this paradoxical trend warrants attention. For individuals with earlier AAM, reproductive lifespan may be shortened because of decreased AMH level in advance and trend toward delayed marriage and childbearing in society [ 33 – 35 ]. Necessary interventions may be implemented to preventing the premature decline of ovarian function. Initially, it is recommended for healthcare professionals to disseminate information to the community about the association between early menarche in children and the subsequent risk of diminished ovarian reserve in adults. Secondly, screening and periodic AMH monitoring are necessary in children/adolescents with an early AAM. Moreover, parents and guardians can help prevent early menarche by fostering healthy habits in children, such as maintaining a balanced diet, engaging in regular exercise, preventing obesity, and minimizing contact with environmental endocrine disruptors [ 59 , 60 ]. Finally, for individuals with early AAM, they should be encouraged to consider the optimal timing for childbearing. This study has several notable strengths. First, we leveraged a nationwide, large-scale epidemiological survey dataset, which included invaluable biological samples for the assessment of AMH levels. Second, to our knowledge, this is the first study to identify the critical transition period in which AAM exerts a significant influence on AMH. Third, we adjusted for a wide range of covariates, including demographic characteristics, baseline characteristics, menstrual status, and marriage and childbearing situation. Our study also has several limitations. First, a limitation of our study is that, as a cross-sectional design, it lacks validation from prospective research. Secondly, the exposure factor, AAM, was assessed by a questionnaire. The retrospective reliance on self-report may have introduced recall bias. Moreover, our study population was exclusively composed of eastern-Asian community-based individuals; therefore, the generalizability of our findings to other populations warrants further investigation. Finally, as the association between AAM and AMH is derived from a population-level correlation study, its underlying mechanisms must be elucidated by biological study to pave the way for precise interventions.

Menarche, which means the maturation of the reproductive axis, is the starting point in women’s reproductive lifespan [ 1 – 3 ]. At birth, females possess a fixed number of follicles, which decline progressively from the prenatal period until menopause. During this process, there is a finite reproductive window that spans from menarche, which means sexual maturation and the first menstruation, to the menopause, which means the final menstruation. The average age at menarche (AAM) is about 12.5 to 14.3 years, normally approximately 2 years after the onset of puberty [ 1 , 4 – 6 ]. Studies have found trends toward earlier menarche during the past 5 to 10 decades globally [ 6 – 13 ], which has been largely attributed to improvement in living conditions and nutritional status [ 14 ]. For example, the mean AAM fell by 0.6 years in the American women from 12.5 years to 11.9 years over approximately 50 years, by 0.18 years from 13.42 years to 13.24 years among Norwegian women born between 1936 and 1964, and by 1 year from 14.3 years to 13.3 years among Chinese women born between 1970 and 1989 [ 6 , 13 , 15 ]. Anti-Müllerian hormone (AMH), which is a member of transforming growth factor superfamily, is secreted by granulosa cells of ovarian growing antral follicles (< 8 mm in diameter) [ 16 , 17 ]. The secretion of AMH is initiated by the female fetus around the 36th week of gestation. Following a peak in young adulthood, its levels undergo a progressive decline, becoming undetectable upon the onset of menopause [ 18 , 19 ]. Furthermore, Chinese researchers utilized a large, representative population sample, and established percentile reference values for AMH across reproductive ages in women [ 20 ]. AMH is positively correlated with the number of follicles remaining in the ovary [ 21 ]. Unlike reproductive hormones such as follicle stimulating hormone (FSH) and lutheinizing hormone (LH), AMH showed no significant difference throughout human menstrual cycle [ 16 ]. Clinically, AMH is the most commonly used and reliable indicator reflecting ovarian reserve function [ 22 – 24 ]. Diminished ovarian reserve (DOR) refers to a condition characterized by a reduction in the quantity and quality of oocytes stored in the ovaries, leading to a decline in female fertility, infertility, assisted reproductive technology failure, and miscarriage. Based on previous literature, the diagnosis is primarily based on decreased AMH level and antral follicle counts, and elevated FSH level [ 25 ]. Decrease AMH level indicates diminished ovarian reserve [ 26 ]. The prevalence of DOR has increased significantly in recent years [ 27 – 30 ]. Some researchers demonstrated that AAM may be a predictor of DOR [ 31 ], indicating a possible association between AAM and AMH. There is an obscure relationship between AAM and AMH. Generally, researchers suggested that among women with a mean age of 38.9 ± 4.9 years, earlier menarche was associated with lower AMH [ 31 ]. However, the study conducted in the Philippines suggested that women who experienced earlier menarche had significantly higher AMH as young adults aged 20 years to 22 years. Although the association between AAM and AMH levels has been previously investigated, the results remain inconclusive. Currently, there is a lack of research on the impact of AAM on AMH level in women across the entire reproductive lifespan [ 32 ].Against the backdrop of declining fertility and the trend toward delayed marriage and childbearing in society, which means the shortening of female reproductive lifespan, it is particularly important to clarify the relationship between AAM and AMH and to implement corresponding interventions [ 33 – 35 ]. Furthermore, it’s also vital to explicit the critical point at which AAM influences AMH remarkably. In this study, we performed a nationwide cross-sectional survey in China to evaluate the relationship between AAM and age-adjusted AMH level in women aged 20–49 years. Additionally, we explored the effect of AAM on AMH in different BMI, menstrual regularity, menstrual cycle length, and subfertility-related conditions such as polycystic ovary syndrome (PCOS), infertility and hypothyroidism.

Supplementary Material 1. Supplementary Material 1. Supplementary Material 2. Supplementary Material 2.