Increased body mass index is associated with a nondilutional reduction in antimüllerian hormone

Context: Controversy exists regarding if and how body mass index (BMI) impacts antimüllerian hormone (AMH) in women with and without polycystic ovary syndrome (PCOS). Understanding the BMI-AMH relationship has critical implications for clinical interpretation of laboratory values and could illuminate underlying ovarian physiology. Objective: To test the hypotheses that (1) BMI is associated with reduced AMH in PCOS and ovulatory controls (OVAs) and (2) the reduction in AMH is not accounted for by dilutional effects. Design/Setting: Multicenter cohort. Participants: Women aged 25 to 40 years from 2 clinical populations: 640 with PCOS, 921 women as OVAs. Main Outcome Measures: Ovarian reserve indices: AMH, antral follicle count (AFC), and AMH to AFC ratio (AMH/AFC) as a marker of per-follicle AMH production. Results: In both cohorts, increasing BMI and waist circumference were associated with reductions in AMH and AMH/AFC, after adjusting for age, race, smoking, and site in multivariate regression models. Increasing BMI was associated with reduced AFC in PCOS but not OVAs. Body surface area (BSA), which unlike BMI is strongly proportional to plasma volume, was added to investigate a potential dilutive effect of body size on AMH concentrations. After controlling for BSA, BMI retained independent associations with AMH in both cohorts; BSA no longer associated with AMH. Conclusions: In an adjusted analysis, BMI, but not BSA, was associated with reduced AMH; these data do not support a role for hemodilution in mediating the relationship between increased body size and reduced AMH. Decreased AMH production by the follicle unit may be responsible for reduced AMH with increasing BMI.