AbstractIntroductionIn this prospective cohort study we aimed to investigate the hypothesis that fluctuations in anti‐Müllerian hormone levels stem from fluctuations in the number of antral follicles.Material and methodsRepeated measurements of anti‐Müllerian hormone and antral follicles (follicles 2–8 mm) were performed in 44 women with a regular cycle, during one menstrual cycle. If our hypothesis that anti‐Müllerian hormone fluctuations stem from fluctuations in the antral follicles is correct, a fluctuation in the antral follicles would result in an equal and parallel shift in anti‐Müllerian hormone. Hence, the difference between antral follicles and anti‐Müllerian hormone would remain constant over time. A mixed model analysis, assessing the stability between anti‐Müllerian hormone and antral follicles, was performed using the difference between _logantral follicles and _loganti‐Müllerian hormone. Cohen's D was calculated for the largest of fixed effects in order to assess stability in relative distance between antral follicles and anti‐Müllerian hormone. To assess if fluctuation in anti‐Müllerian hormone or antral follicles originated from between‐subject fluctuation, or from within subject fluctuation, the intra‐class correlation coefficient was calculated.ResultsMixed model analysis and Cohen's D (0.12) confirmed the stability of the difference between _logantral follicles and _loganti‐Müllerian hormone and so confirmed our hypothesis. The good intra‐class correlation coefficient (0.73) indicated a small contribution of within‐subject variation to anti‐Müllerian hormone fluctuations.ConclusionsFluctuations in anti‐Müllerian hormone levels parallel fluctuations in antral follicles, suggesting that anti‐Müllerian hormone levels are closely linked to variation in the antral follicles. This knowledge adds to the basic understanding of the origin of anti‐Müllerian hormone and could aid in interpretation of individual anti‐Müllerian hormone levels.