The measurement of circulating anti-Müllerian hormone (AMH) has been applied to a wide array of clinical applications, mainly based on its ability to reflect the number of antral and pre-antral follicles present in the ovaries. AMH has been suggested to predict the ovarian response to hyperstimulation of the ovaries for IVF and the timing of menopause, and to indicate iatrogenic damage to the ovarian follicle reserve. It has also been proposed as a surrogate for antral follicle count (AFC) in the diagnosis of polycystic ovary syndrome (PCOS). This paper is a summary of presentations at a European Society of Human Reproduction and Embryology campus workshop on AMH, with literature cited until September 2013. Published peer-reviewed medical literature about AMH was searched through MEDLINE and was subjected to systematic review and critical assessment by the panel of authors. Physiologically, recent data confirm that AMH is a follicular gatekeeper limiting follicle growth initiation, and subsequently estradiol production from small antral follicles prior to selection. AMH assays continue to evolve and technical issues remain; the absence of an international standard is a key issue. The dynamics of circulating AMH levels throughout life can be split into several distinct phases, with a peak in the early 20s before a decline to the menopause, with a strong and positive correlation with non-growing follicle recruitment. There is a more complex rise during childhood and adolescence, which is likely to be more reflective of different stages of follicle development. AMH shows limited short-term variability, but the influence of states such as prolonged oral contraceptive use need to be considered in clinical assessment. There are only very limited data on relationships between AMH and natural fertility at different stages of reproductive life, and while it has a relationship to age at menopause the marked variability in this needs further exploration. AMH may be useful in assessing the need for fertility preservation strategies and detecting post-chemotherapy or surgical damage to the ovarian reserve. Long-term follow-up of patients to ascertain fully the value of post-cancer serum AMH in predicting long-term ovarian function is required. There is a linear relationship between AMH and oocyte yield after ovarian stimulation, which is of value in predicting ovarian hyperstimulation. AMH can also identify ‘poor responders’, but it seems inappropriate at present to withhold IVF purely on this basis. Women with PCOS show markedly raised AMH levels, due to both the increased number of small antral follicles and intrinsic characteristics of those granulosa cells, and this may contribute to anovulation. The value of AMH in the diagnosis of PCOS remains controversial, but it may replace AFC in the future. For the first time in female reproductive biology, it is possible to measure the submerged part of the iceberg of follicle growth, i.e. the intrinsic, so-called ‘acyclic’ ovarian activity. An international standard for AMH and improved assay validity are urgently needed to maximize the clinical utility of this very promising biomarker of ovarian function in a large array of clinical situations, both in childhood and adulthood.

The polycystic ovary syndrome (PCOS) is a heterogeneous condition, the pathophysiology of which appears to be both multifactorial and polygenic. The definition of the syndrome has been much debated. Key features include menstrual cycle disturbance, hyperandrogenism and obesity. There are many extra‐ovarian aspects to the pathophysiology of PCOS, yet ovarian dysfunction is central. At a recent joint ASRM/ESHRE consensus meeting, a refined definition of the PCOS was agreed, encompassing a description of the morphology of the polycystic ovary (PCO). According to the available literature, the criteria fulfilling sufficient specificity and sensitivity to define the PCO should have at least one of the following: either 12 or more follicles measuring 2–9 mm in diameter, or increased ovarian volume (>10 cm³). If there is a follicle >10 mm in diameter, the scan should be repeated at a time of ovarian quiescence in order to calculate volume and area. The presence of a single PCO is sufficient to provide the diagnosis. The distribution of follicles and a description of the stroma are not required in the diagnosis. Increased stromal echogenicity and/or stromal volume are specific to PCO, but it has been shown that the measurement of ovarian volume (or area) is a good surrogate for quantification of the stroma in clinical practice. A woman having PCO in the absence of an ovulation disorder or hyperandrogenism (‘asymptomatic PCO’) should not be considered as having PCOS, until more is known about this situation. Three‐dimensional and Doppler ultrasound studies may be useful research tools but are not required in the definition of PCO. This review outlines evidence for the current ultrasound definition of the polycystic ovary and technical specifications.

The serum level of anti-Mullerian hormone (AMH), a product from granulosa cells involved in follicle growth, has been shown to correlate tightly with the small antral follicle number (FN) at ultrasonography (U/S) in women who do not have polycystic ovary syndrome (PCOS). Because PCOS is associated with a 2- to 3-fold increase in growing FN, we investigated whether an increased AMH serum level correlates to other hormonal and/or U/S features of PCOS. Serum AMH has been assayed in 104 women (59 symptomatic PCOS, 45 controls) between d 2 and 7 after the last either spontaneous or progestin-induced (in PCOS) menstrual period. Mean serum AMH level was markedly increased in the PCOS group (47.1 ± 22.9 vs. 20.8 ± 11.6 pmol/liter in controls; P < 0.0001), an increase in the same order of magnitude as the one of the FN in the 2- to 5-mm range at U/S (12.8 ± 8.3 vs. 4.8 ± 1.9; P < 0.0001, respectively). The ratio AMH/FN was similar between the two groups (4.8 ± 3.4 vs. 4.8 ± 2.9; P = 0.55). By simple regression, both in PCOS and controls, the AMH level was positively related to the 2- to 5-mm FN at U/S (P < 0.0001 and P < 0.03, respectively), but not to the 6- to 9-mm FN, and was negatively correlated to the serum FSH level (P < 0.02 and P < 0.04, respectively). AMH was also positively related to the serum testosterone and androstenedione levels, in PCOS exclusively (P < 0.0005 and <0.002, respectively). No relationship was found between AMH and age, serum estradiol, inhibin B, and LH levels in both groups. After multiple regression only the 2- to 5-mm FN remained significantly related to AMH in PCOS whereas testosterone, androstenedione, and FSH were no longer. In conclusion, the assay of the serum AMH may represent an important breakthrough in the diagnosis and in the understanding of PCOS. Our data suggest that the increase of AMH serum level in PCOS is the consequence of the androgen-induced excess in small antral FN and that each follicle produces a normal amount of AMH. We hypothesize that an increased AMH tone within the cohort could be involved in the follicular arrest of PCOS, by interacting negatively with FSH at the time of selection.

Polycystic ovary syndrome (PCOS) is the most common ovarian disorder associated with androgen excess in women, which justifies the growing interest of endocrinologists. Great efforts have been made in the last 2 decades to define the syndrome. The presence of three different definitions for the diagnosis of PCOS reflects the phenotypic heterogeneity of the syndrome. Major criteria are required for the diagnosis, which in turn identifies different phenotypes according to the combination of different criteria. In addition, the relevant impact of metabolic issues, specifically insulin resistance and obesity, on the pathogenesis of PCOS, and the susceptibility to develop earlier than expected glucose intolerance states, including type 2 diabetes, has supported the notion that these aspects should be considered when defining the PCOS phenotype and planning potential therapeutic strategies in an affected subject. This paper offers a critical endocrine and European perspective on the debate on the definition of PCOS and summarises all major aspects related to aetiological factors, including early life events, potentially involved in the development of the disorder. Diagnostic tools of PCOS are also discussed, with emphasis on the laboratory evaluation of androgens and other potential biomarkers of ovarian and metabolic dysfunctions. We have also paid specific attention to the role of obesity, sleep disorders and neuropsychological aspects of PCOS and on the relevant pathogenetic aspects of cardiovascular risk factors. In addition, we have discussed how to target treatment choices based according to the phenotype and individual patient's needs. Finally, we have suggested potential areas of translational and clinical research for the future with specific emphasis on hormonal and metabolic aspects of PCOS.

BACKGROUND Androgens, FSH, anti-Müllerian hormone (AMH) and estradiol (E2) are essential in human ovarian folliculogenesis. However, the interactions between these four players is not fully understood. OBJECTIVES AND RATIONALE The purpose of this review is to highlight the chronological sequence of the appearance and function of androgens, FSH, AMH and E2 and to discuss controversies in the relationship between FSH and AMH. A better understanding of this interaction could supplement our current knowledge about the pathophysiology of the polycystic ovary syndrome (PCOS). SEARCH METHODS A literature review was performed using the following search terms: androgens, FSH, FSH receptor, anti-Mullerian hormone, AMHRII, estradiol, follicle, ovary, PCOS, aromatase, granulosa cell, oocyte. The time period searched was 1980–2015 and the databases interrogated were PubMed and Web of Science. OUTCOMES During the pre-antral (‘gonadotropin-independent’) follicle growth, FSH is already active and promotes follicle growth in synergy with theca cell-derived androgens. Conversely, AMH is inhibitory by counteracting FSH. We challenge the hypothesis that AMH is regulated by androgens and propose rather an indirect effect through an androgen-dependent amplification of FSH action on granulosa cells (GCs) from small growing follicles. This hypothesis implies that FSH stimulates AMH expression. During the antral (‘gonadotropin-dependent’) follicle growth, E2 production results from FSH-dependent activation of aromatase. Conversely, AMH is inhibitory but the decline of its expression, amplified by E2, allows full expression of aromatase, characteristic of the large antral follicles. We propose a theoretical scheme made up of two triangles that follow each other chronologically. In PCOS, pre-antral follicle growth is excessive (triangle 1) because of intrinsic androgen excess that renders GCs hypersensitive to FSH, with consequently excessive AMH expression. Antral follicle growth and differentiation are disturbed (triangle 2) because of the abnormally persisting inhibition of FSH effects by AMH that blocks aromatase. Beside anovulation, this scenario may also serve to explain the higher receptiveness to gonadotropin therapy and the increased risk of ovarian hyperstimulation syndrome (OHSS) in patients with PCOS. WIDER IMPLICATIONS Within GCs, the balance between FSH and AMH effects is pivotal in the shift from androgen- to oestrogen-driven follicles. Our two triangles hypothesis, based on updated data from the literature, offers a pedagogic template for the understanding of folliculogenesis in the normal and polycystic ovary. It opens new avenues for the treatment of anovulation due to PCOS.