Age-related decline in AMH and gonadotropin patterns in Syrian women: Preliminary population-based estimates

Abstract

Background

Anti-Müllerian hormone (AMH) is a key biomarker of ovarian reserve, yet population-specific reference values remain limited for Middle Eastern women.

Objectives

Establishing preliminary age-specific population estimates of AMH and gonadotropin is essential for improving clinical interpretation in this demographic.

Design

Cross-sectional, population-based exploratory study conducted between March 2025 and February 2026.

Methods

90 healthy women aged 19–47 years were recruited. Serum AMH, follicle-stimulating hormone (FSH), and luteinizing hormone (LH) were measured on cycle day 3. Age-specific distributions were summarized as preliminary population-based estimates, given the modest sample size within each age stratum. Linear regression models were used to assess whether AMH independently predicted FSH, LH, or the LH/FSH ratio after adjusting for age.

Results

AMH showed a strong inverse correlation with age (r=–0.54). ROC analysis demonstrated that lower AMH levels were strongly associated with being older than 35 years, with an AMH value of 1.8 ng/mL (AUC≈0.80; sensitivity 0.94; specificity 0.61), indicating high sensitivity but limited specificity. FSH increased progressively with age (r=0.29), while LH remained relatively stable, resulting in a declining LH/FSH ratio. Regression analysis showed that AMH was independently associated with the LH/FSH ratio (β = 0.100, p < 0.001), but not FSH or LH after adjusting for age.

Conclusion

This study provides the first preliminary age-specific population estimates of AMH and gonadotropins in Syrian women, demonstrating patterns consistent with global ovarian-aging trajectories. However, the absence of data on BMI, smoking, and lifestyle factors, along with the modest sample size, may limit the precision and generalizability of these estimates.

Plain language summary

This study looked at how ovarian reserve changes with age in healthy Syrian women. We measured three hormones that help show ovarian reserve: anti Müllerian hormone (AMH), follicle stimulating hormone (FSH), and luteinizing hormone (LH). All tests were done on day 3 of the menstrual cycle, when these hormones are most stable. AMH is the most reliable marker of ovarian reserve. In this study, AMH levels were high in younger women and dropped steadily with age. Women aged 19–25 had much higher AMH levels than women aged 41–47. An AMH level of 1.8 ng/mL was strongly linked to being 35 years or older, meaning this value may help identify women whose ovarian reserve has begun to decline. FSH increased with age. Younger women usually had FSH levels below 10 mIU/mL, while women over 40 often had levels above 15 mIU/mL. Higher FSH levels indicate that the ovaries are working harder to produce eggs, which happens as ovarian reserve decreases. LH changed only slightly with age. Because FSH rises more than LH, the LH/FSH ratio became lower in older women. Younger women typically had ratios close to or above 1.0, while women over 35 often had ratios below 0.40. Overall, the study shows that AMH, FSH, and the LH/FSH ratio change in predictable ways as women age. These results provide the first population specific hormone estimates for Syrian women and can help doctors better interpret ovarian reserve in this region. However, the study did not include information on body weight, smoking, or lifestyle, and the sample size was modest, so larger studies are still needed.

Introduction

Ovarian reserve declines progressively with age, and timely identification of reduced reserve is critical for fertility planning, infertility management, and counseling regarding reproductive lifespan. ¹ Anti-Müllerian hormone (AMH) has emerged as a key biomarker of ovarian reserve, reflecting the size of the growing follicle pool and declining earlier and more gradually than traditional gonadotropin markers such as follicle-stimulating hormone (FSH) and luteinizing hormone (LH). ² AMH is a dimeric glycoprotein produced by granulosa cells of pre-antral and small antral follicles, ³ where it plays a key regulatory role in early folliculogenesis and serves as a direct indicator of the size of the growing follicle pool. ⁴ Unlike FSH and LH, which are influenced by short-term cycle variability and hypothalamic–pituitary feedback, AMH is relatively cycle-independent and more directly linked to follicular quantity, yet gonadotropins remain widely used in clinical practice, making it important to understand their joint behavior across reproductive aging. ⁵

Because AMH reflects the functional ovarian follicle pool, it has become central to modern reproductive endocrinology. It is widely used to assess ovarian reserve, predict ovarian response to stimulation, estimate reproductive lifespan, and guide fertility counseling. ⁶ Large cohort studies have demonstrated that AMH declines steadily across reproductive life and often identifies diminished ovarian reserve earlier than FSH or menstrual cycle changes.^7–9 As a result, AMH is now incorporated into clinical guidelines for infertility evaluation, assisted reproduction, and anticipatory fertility counseling. ¹⁰ Despite its widespread use, AMH interpretation requires population-specific reference ranges, as values vary significantly across ethnicities, assay platforms, and demographic groups.

Ethnicity influences both baseline AMH levels and the tempo of decline. Reviews show that AMH tends to be lower in Black and Hispanic women and higher in Chinese women before age 25 compared with age-matched Caucasian women. ¹¹ These differences underscore the importance of establishing population-specific reference ranges. Studies comparing European, South Asian, and African populations have consistently demonstrated distinct AMH distributions and age-related trajectories, suggesting that applying reference values derived from other populations may lead to misclassification of ovarian reserve status.^12,13 Establishing normative AMH and gonadotropin values for Middle Eastern populations is therefore essential for accurate clinical interpretation.

Data from Arab and Middle Eastern populations remain limited, with only a few country-specific reports and no comprehensive regional reference standards. Existing studies from Lebanon, Saudi Arabia, Egypt, Turkey and Iran provide valuable insights but are restricted by small sample sizes, clinical subgroups, or lack of age-stratified normative ranges.^14–18 To our knowledge, only one study from Syria has examined ovarian reserve using AMH, focusing on age at menarche as a predictor of low AMH levels. ¹⁹ However, no prior Syrian research has established age-specific AMH reference ranges or evaluated gonadotropin dynamics across the reproductive lifespan. Furthermore, the independent contribution of AMH to FSH, LH, and their ratios has not been characterized in this population, despite its relevance for understanding endocrine adaptations of ovarian aging. These gaps highlight the need for population-based hormonal reference values that reflect the unique demographic, genetic, and environmental characteristics of Syrian women.

Therefore, the present study aimed to establish preliminary age-specific population estimates of AMH, FSH, LH, and the LH/FSH ratio in healthy Syrian women, and evaluate AMH as an independent predictor of gonadotropin dynamics across reproductive aging. By providing the first population-based hormonal reference dataset for Syrian women, this study offers clinically relevant benchmarks for ovarian reserve assessment and reproductive counseling in this region.

Methods

Study subjects

The cross-sectional study was conducted at Tartous Medical Center in Syria between March 2025 till February 2026 based on availability sampling strategy. Because the study was exploratory and based on the accessible population, no formal power analysis was performed. A total of 90 healthy volunteer women aged 19–47 years with both ovaries intact from the outpatient gynecology clinic were recruited. The age range of 19–47 years was selected to represent the full reproductive lifespan while excluding adolescent and women in the perimenopausal transition, where cycle irregularity and endocrine variability limit the establishment of stable reference values. Age groups were stratified into clinically meaningful 5–7-year intervals to ensure adequate sample size and to generate age-specific reference ranges. All participants reported regular menstrual cycles (24–35 days) and were not taking any medication known to affect sex hormones or metabolism within the past 6 months, and reported no history of chronic, metabolic, or endocrine disorder. Women with a history of ovarian surgery, chemotherapy, radiotherapy, or known ovarian pathology were excluded to avoid confounding effects on ovarian reserve markers.

The study protocol was approved by the Ethics Committee of Wadi International University (Approval No. 073-2025, granted on 7 March 2025) and written informed consent was obtained from all participants in accordance with the Helsinki II ethical guidelines. ²⁰ The reporting of this study conforms to the STROBE statement. ²¹

Biochemical assay

The biochemical evaluation included serum follicle-stimulating hormone (FSH, mlU/ml), luteinizing hormone (LH, mlU/ml), and anti-Müllerian hormone (AMH, ng/ml). Peripheral venous blood samples were collected in the early morning, and all samples were drawn on day 3 of the menstrual cycle to minimize physiological variability in gonadotropin levels. ²² Samples were processed within two hours of collection, centrifuged at 3000 rpm for 10 minutes, and serum aliquots were stored at -20°C until analysis to preserve biomarker stability. Serum LH and FSH were measured using automated chemiluminescent immunoassays (Roche Cobas e411), ²³ while serum AMH was measured by enzyme-linked immunosorbent assay (ELISA) using a two-site ELISA kit (Beckman Coulter AMH Gen II). ²⁴ All assays were performed in accordance with the manufacturers’ instructions and under strict laboratory quality-control procedures.

Statistical analysis

All statistical analyses were performed using standard procedures for cross-sectional hormonal data. Continuous variables were assessed for normality and summarized as medians with interquartile ranges due to their non-Gaussian distribution. Group comparisons across age categories were conducted using appropriate non-parametric tests. Associations between hormonal markers and age were evaluated using Spearman’s rank correlation coefficients, and correlation matrices were constructed to examine inter-relationships among AMH, FSH, LH, and derived ratios (FSH/LH and LH/FSH). Linear regression models were applied to assess the independent association of AMH with FSH, LH, and gonadotropin ratios after adjusting for age. To evaluate the performance of AMH in identifying the physiological transition into late reproductive age (defined clinically as age>35 years), receiver operating characteristic (ROC) curve analysis was conducted. The optimal AMH cutoff value was determined by maximizing Sensitivity and Specificity (Youden’s J index). Logistic regression was applied to quantify the association between AMH levels and the likelihood of being in the late reproductive age category (age>35 years) within this preliminary cohort. Statistical significance was defined as a two-tailed p value < 0.05.

Results

A total of 90 women aged 19–47 years were included. The distribution across age groups was as follows: 19–25 years (n=23), 26–30 years (n=20), 31–35 years (n=15), 36–40 years (n=17), and 41–47 years (n=15), (Table 1).

Table 1.

Demographic characteristics of the study population.

Total sample size	90
Age range (years)	19-47
Age group distribution	19–25 years: 23
	26–30 years: 20
	31–35 years: 15
	36–40 years: 17
	41–47 years: 15
Menstrual cycle regularity	Regular cycles (24–35 days)
Medication affecting hormones (past 6 months)	None reported
Chronic, metabolic, or endocrine disorders	None reported
History of ovarian surgery/chemotherapy/radiotherapy	None reported
BMI	Not collected
Smoking status	Not collected
Lifestyle factors	Not collected

AMH showed a strong inverse association with age (r=–0.54). Median AMH declined from 3.79 ng/mL in women aged 19–25 years to 0.39 ng/mL in women aged 41–47 years, corresponding to an estimated annual decline of approximately 0.15 ng/mL as presented in Table 2. The prevalence of diminished ovarian reserve increased from 21% in the youngest group to 100% in the oldest group as presented in Figure 1.

Figure 2.

Receiver operating characteristic (ROC) curve for AMH as a discriminator of age > 35 years.

Table 2.

Distribution of Anti-Müllerian Hormone (AMH) levels across age groups.

Age group (years)	N	Median (ng/mL)	IQR (25–75%)	Range (min–max)
19–25	23	3.79	2.44 – 5.6	0.14 – 10.20
26–30	20	2.98	1.75 – 4.78	0.17 – 11.32
31–35	15	1.48	0.68 – 2.82	0.14 – 5.77
36–40	17	0.51	0.39 – 1.08	0.10 – 7.90
41–47	15	0.45	0.2 – 0.94	0.11 – 1.80

Figure 1.

Presence of diminished ovarian reserve in each age group. ROC analysis as illustrated in Figure 2 was performed to assess the capacity of AMH to discriminate between early and late reproductive age strata (>35$ years). An AMH threshold of 1.8 ng/mL demonstrated an area under the curve (AUC) of 0.80, with a high sensitivity of 0.94 and a moderate specificity of 0.61. This indicates that while an AMH level below 1.8 ng/mL effectively captures the vast majority of women in the ≥ 35 age group, a subset of younger women also exhibited levels below this threshold. In logistic regression modeling, lower AMH levels were significantly associated with the late reproductive age category (β = -0.697, p < 0.001; Likelihood Ratio Test p < 0.0001), confirming the sharp age-dependent shift in ovarian reserve in this demographic.

In contrast, FSH levels increased progressively with age (r=0.29), rising from a median of 7.45 mIU/mL in the youngest group to 15.24 mIU/mL in women older than 40 years (Table 3). A cutoff of FSH ≥ 10 mIU/mL effectively separated women older than 30 from younger subjects, while FSH ≥ 15 mIU/mL identified women with markedly diminished ovarian reserve.

Table 3.

Distribution of Follicle-Stimulating Hormone (FSH) levels across age groups.

Age group (years)	n	Median (mIU/mL)	IQR (25–75%)	Range (min–max)
19–25	23	7.45	6.25 – 10.48	4.77 – 51
26–30	20	6.745	5.85 – 8.25	3.14 – 14.9
31–35	15	11.24	7.24 – 13.37	4.86 – 34.8
36–40	17	10.98	6.31 – 12.99	3.74 – 24.6
41–47	15	14.7	11.32 – 40.43	5.81 – 72

LH exhibited a modest age-related increase, with a weak negative correlation between LH and age (r=-0.02). As a result, the LH/FSH ratio decreased progressively with age (r=-0.29), reflecting the disproportionate rise in FSH relative to LH as ovarian follicular reserve diminishes with age. In this study, younger women (≤30 years) generally exhibited LH/FSH ratios close to or above 1.0, whereas women older than 35 showed markedly reduced ratios, often below 0.40 (Table 4).

Table 4.

Distribution of LH/FSH ratio across age groups.

Age group (years)	n	Median LH/FSH	IQR (25–75%)	Range (min–max)
19–25	23	0.77	0.55 – 1.30	0.35 – 2.83
26–30	20	1.01	0.79 – 1.30	0.27 – 3.41
31–35	15	0.63	0.45 – 0.81	0.14 – 1.02
36–40	17	0.75	0.63 – 1.05	0.24 – 1.39
41–47	15	0.67	0.38 – 0.83	0.08 – 1.5

A linear regression analysis was proceeded to evaluate the independent association between AMH and gonadotropins, adjusted for age. Results showed that AMH was not an independent predictor of FSH after adjusting for age (β = –1.21, p = 0.25), whereas age remained a significant positive predictor (β = 0.86, p = 0.012). For LH, neither age nor AMH showed significant associations (Age: β = 0.089, p = 0.29; AMH: β = 0.086, p = 0.74), and the model explained only 1.2% of the variance (R² = 0.012), indicating that LH remains relatively stable across reproductive aging. In contrast, AMH was independently associated with the LH/FSH ratio (β = 0.100, p < 0.001), while age showed no significant effect (β = –0.0068, p = 0.37), with the model accounting for 24% of the variance in LH/FSH (R² = 0.24).

Discussion

Ethnic and population-specific differences in AMH levels and decline rates have been documented, underscoring the importance of establishing local reference ranges. A comprehensive review reported substantial ethnic and race-related differences in AMH, noting that Black and Hispanic women tend to have lower AMH, while Chinese women have higher AMH before age 25 compared with age-matched Caucasian women. These differences persist even after adjusting for age and reproductive characteristics. ¹¹ A cross-sectional comparison of Spanish and Indian women undergoing IVF demonstrated lower AMH levels in Spanish women, despite being older on average, suggesting distinct ovarian aging trajectories between ethnicities. ²⁵ A study comparing Indian and Ethiopian women found significantly higher AMH levels in Indian women, with a stronger negative correlation between AMH and age in Ethiopian women, reinforcing that ethnicity influences both baseline AMH and the rate of decline. ²⁶ These variations highlight the value of generating population-based AMH norms for Syrian women, providing clinically relevant benchmarks for interpreting ovarian reserve in this demographic.

In this context, the age-related decline observed in Syrian women aligns with global findings. Large cohort studies consistently demonstrate a steady reduction in AMH across reproductive life, with clinically relevant thresholds emerging in the mid-thirties. Large cohort studies confirm that AMH decreases steadily across reproductive life, with median values falling below approximately 1.0–1.2 ng/mL in the mid-thirties. Although the AMH cutoff of 1.8 ng/mL is slightly higher than the 1.0–1.2 ng/mL thresholds commonly reported in large international cohorts, it still reflects the same early-to-mid-thirties inflection point in ovarian reserve decline. A comprehensive age-stratified analysis of 22,920 women showed a significant negative correlation between age and AMH, with median AMH levels falling steadily and dropping below 1.2 ng/mL by age 36. ²⁷ Additional large-scale studies reinforce this trend, showing that AMH levels decrease progressively as women approach menopause, reflecting the depletion of the ovarian follicle pool. ²⁸ Another cross-sectional study of fertile and infertile Indian women similarly demonstrated age-dependent reductions in AMH and identified early-thirties thresholds for accelerated decline. ²⁹ Similar ROC-based age thresholds have been reported in other populations, where the early thirties represent a critical inflection point in ovarian reserve decline. In Indian cohorts, ROC analysis identified age cutoffs of approximately 31–34 years for significant reductions in AMH and AFC, supporting the notion that early-thirties transitions in ovarian reserve are biologically conserved across ethnicities. This convergence strengthens the clinical relevance of age-based AMH thresholds for early identification of women at risk for diminished ovarian reserve. ²⁹ Physiological reviews also describe an acceleration in follicular depletion beginning in the mid-to-late thirties. ³⁰ In the present study, rather than serving as a diagnostic tool for chronological age itself, the ROC-derived threshold of 1.8 ng/mL highlights the biochemical transition point corresponding to the clinical threshold of 35 years in Syrian women. The high sensitivity (0.94) confirms that AMH markedly declines by age 35, while the moderate specificity (0.61) reflects individual physiological variability in ovarian reserve—namely, identifying younger women who experience prematurely reduced AMH levels. This aligns with ROC-based age thresholds reported in other populations, where the early-to-mid thirties represent a critical inflection point in follicular depletion.

The clear age-dependent increase of FSH levels reflects the physiological loss of ovarian negative feedback as follicular reserve declines. The positive correlation between FSH and age (r=0.29) is consistent with the classical endocrine response to diminishing granulosa-cell function, in which declining inhibin B and estradiol secretion reduces negative feedback on the hypothalamic–pituitary axis, leading to compensatory elevations in circulating FSH. ³¹ Median FSH rose from 7.45 mIU/mL in women aged 19–25 years to 15.24 mIU/mL in those older than 40 years, mirroring the steep decline in AMH observed across the same age range. These findings align with established literature showing that FSH increases progressively with age and accelerates during the late reproductive transition.^32,33 Longitudinal endocrine studies have demonstrated that rising FSH is one of the earliest biochemical markers of ovarian aging, often preceding menstrual cycle changes by several years. ³⁴ Clinical thresholds such as FSH ≥ 10 mIU/mL have been widely used to identify diminished ovarian reserve, while values ≥ 15 mIU/mL are strongly associated with poor ovarian response and reduced fertility potential.^35,36

LH exhibited a modest age-related increase, which is expected because LH secretion is less sensitive to declining ovarian inhibin B and estradiol compared with FSH, and LH typically remains relatively stable until later stages of reproductive aging. ³⁷ Median LH values remained within the normal physiological range across age groups, with only subtle upward shifts in women over 40 years. As a result, the LH/FSH ratio decreased progressively which aligns with the physiological shift toward increased pituitary drive in response to diminished granulosa-cell feedback.

Together, the modest increase in LH, the strong rise in FSH, and the declining LH/FSH ratio complement the observed age-related decline in AMH, reinforcing the coordinated endocrine adaptations that characterize ovarian aging. Studies across diverse populations have consistently demonstrated that the relative stability of LH with age, contrasted with a sharper rise in FSH and a progressive decline in the LH/FSH ratio—is a conserved endocrine feature of reproductive aging. Foundational work in European and North American cohorts has shown that LH exhibits only modest age-related changes, whereas FSH increases markedly as ovarian inhibin B and estradiol decline, leading to a characteristic reduction in the LH/FSH ratio.^37,38 More recent large-scale population studies reinforce this trajectory across different ethnic groups. In Indian women, normative hormonal data from the ICMR-PCOS Task Force demonstrated that FSH rises steadily with age while LH remains comparatively stable, resulting in a declining LH/FSH ratio across the reproductive lifespan. ³⁹ Additional Indian data establishing age-specific AMH and gonadotropin reference intervals similarly confirm that LH shows minimal age-related variation, whereas FSH increases more prominently. ⁴⁰ Comparable findings have been reported in East Asian populations. In a large Korean cohort of 2,879 regularly menstruating women, LH values remained relatively constant across age groups, while FSH increased progressively, mirroring the decline in ovarian reserve. ⁴¹ A recent cross-sectional analysis of healthy Chinese individuals further supports this pattern, showing stable LH secretion across age alongside a pronounced rise in FSH, again producing a declining LH/FSH ratio. ⁴²

This study also evaluates AMH as an independent predictor of gonadotropin dynamics across reproductive aging, with FSH, LH, and LH/FSH serving as secondary contextual markers. Findings indicate that AMH contributes substantially to the variability in gonadotropin ratios, capturing physiological components of ovarian aging that are not fully explained by chronological age alone.^35,36 Because AMH directly reflects the size of the growing follicle pool, it provides a more proximal measure of ovarian aging than gonadotropins. ²³ The positive association between AMH and the LH/FSH ratio, demonstrates that AMH effectively reflects the compensatory pituitary responses that accompany follicular depletion.

Limitations

Taken together, these findings provide the first preliminary age-specific population estimates of AMH and gonadotropins in Syrian women, contributing important population-specific data to the global literature on ovarian aging. However, several limitations should be considered when interpreting the results. This study did not collect information on BMI, smoking status, or other lifestyle factors that may influence ovarian reserve, and future studies incorporating these variables would provide a more comprehensive assessment of factors influencing AMH and gonadotropin patterns in this population. In addition, the sample consisted of 90 participants distributed across five age groups, resulting in relatively small subgroup sizes, particularly at the extremes of the reproductive age range. This limits the precision of age-specific reference estimates, particularly at the younger and older extremes of the reproductive age range, and may reduce the generalizability of the findings. Despite these constraints, the study provides clinically relevant hormonal benchmarks and reinforces the biological consistency of age-related ovarian reserve decline across diverse populations.

Conclusion

This study provides preliminary age-specific population estimates of AMH, FSH, and the LH/FSH ratio in healthy Syrian women, offering population-specific benchmarks for assessing ovarian reserve. Lower AMH levels were strongly associated with being older than 35 years, with an AMH cutoff value of 1.8 ng/mL, while FSH thresholds of ≥10 mIU/mL and ≥15 mIU/mL effectively distinguished women older than 30 years and those with markedly diminished ovarian reserve, respectively. Younger women (≤30 years) generally exhibited LH/FSH ratios close to or above 1.0, whereas women older than 35 showed substantially reduced ratios, often below 0.40, consistent with the disproportionate increase in FSH with age. Given the limited data available from Middle Eastern populations, this study fills an important regional gap by generating population-specific AMH and gonadotropin reference values for Syrian women. Although the sample covered the full reproductive age range, the modest sample size and lack of lifestyle or environmental data may limit generalizability. Overall, the coordinated decline in AMH, rise in FSH, and reduction in the LH/FSH ratio highlight the endocrine signatures of ovarian aging in Syrian women and underscore the value of AMH as the most informative biomarker for assessing reproductive aging in this population.

ORCID iDs

Wissam Zam https://orcid.org/0000-0002-2733-1884

Sarah Housheh https://orcid.org/0009-0009-5760-1898

Hajar Marouf https://orcid.org/0009-0008-6231-6680

Jana Alshaer https://orcid.org/0009-0001-4601-7778

Alen Nouman https://orcid.org/0009-0004-8550-0166

Ethical considerations

The study protocol was approved by the Ethics Committee of Wadi International University (Approval No. 073-2025; granted on 7 March 2025).

Consent to participate

Written informed consent was obtained from all participants prior to inclusion in the study, in accordance with the ethical principles of the Declaration of Helsinki.

Consent for publication

No identifying personal data or images of participants are included in this manuscript.

Data Availability Statement

The data are available from the corresponding author upon request.*