The paradoxical association between endometrioma size and serum anti-Müllerian hormone levels in infertile women

The impact of endometrioma size on ovarian reserve remains controversial. Although endometriomas are known to reduce anti-Müllerian hormone (AMH) levels, some studies suggest a paradoxical association between larger cysts and higher AMH. This cross-sectional study enrolled 210 infertile women between January 2023 and March 2025: 150 with laparoscopy-confirmed untreated unilateral endometriomas and 60 controls with male-factor infertility and normal ovaries. Serum AMH, follicle-stimulating hormone, luteinizing hormone, and prolactin were measured on cycle day 3. Endometrioma diameter was measured by transvaginal ultrasound. AMH levels were compared across cyst size categories (≤ 30 mm, 31-50 mm, > 50 mm) using one-way analysis of variance and multiple linear regression, adjusting for age and follicle-stimulating hormone. Mean AMH levels did not differ significantly between the endometrioma and control groups (2.24 ± 1.90 vs. 2.38 ± 1.45 ng/mL; p = 0.30). Within the endometrioma cohort, AMH increased with cyst size (F = 4.98, p = 0.008): 1.72 ± 1.26 ng/mL (≤ 30 mm), 2.23 ± 1.78 ng/mL (31-50 mm), and 2.70 ± 1.69 ng/mL (> 50 mm). Post hoc analysis showed significantly higher AMH in cysts > 50 mm compared with ≤ 30 mm (p = 0.01). In multivariable regression analysis, cyst diameter independently predicted AMH levels (β = 0.031, p < 0.001). Larger endometriomas were paradoxically associated with higher AMH levels. Interpretation of AMH in women with endometriomas should be context-dependent, and clinical decisions regarding ovarian reserve should not rely solely on cyst size or AMH values.