Anti-Mullerian Hormone as a Surrogate Diagnostic Marker for Polycystic Ovary Syndrome

INTRODUCTION

Polycystic ovary syndrome (PCOS) is the commonest gynae-endocrine disorder affecting approximately 6%–13% of women in the reproductive age group globally.^[1] Ganie MA, et al.^[2] did a study amongst women in India to observe the prevalence and comorbidities of PCOS. They found the PCOS prevalence as 7.2% (95% CI, 4.8%–10.8%) according to NIH 1990 criteria, 19.6% (95% CI, 12.7%–29.2%) as per Rotterdam 2003 criteria, and 13.6% (95% CI, 8.4%–21.6%) by Androgen Excess and PCOS Society (AE-PCOS) criteria.^[2]

PCOS is a heterogeneous disorder comprising anovulation, androgen excess and ultrasound findings suggestive of polycystic ovaries. It is a common cause of normogonadotropic anovulation. It is associated with menstrual irregularities, infertility, acne, hirsutism and obesity, which can impact women’s physical as well as emotional health. It is associated with long-term complications like metabolic syndrome, cancer of the uterus and coronary artery disease. As many as 70% of women with PCOS remain undiagnosed.^[1] The diagnosis of PCOS has been evolving over the years, and various criteria have emerged. The Rotterdam’s criteria have been modified to an evidence-based criterion, including the original clinical criteria but a more defined and specific ultrasound criterion for polycystic ovarian morphology (PCOM). In PCOS, there is increased ovarian follicle count, mainly the preantral and small antral follicles in the ovaries, as well as raised serum Anti-Mullerian Hormone (AMH) levels. There exists a positive correlation between serum AMH levels and antral follicle count seen on ultrasound; hence, AMH may be considered as an alternative marker for PCOM in diagnosing PCOS.

DIAGNOSTIC CRITERIA FOR PCOS

Various criteria for diagnosing PCOS have evolved over the years [Table 1]. The first classification emerged from a conference held in April 1990, at a National Institute of Child Health and Human Development of the US,^[3] where hyperandrogenism (HA), either clinical or biochemical, and chronic oligo-anovulation (OA) were described as prime criteria for diagnosing PCOS after excluding other related hyperandrogenic disorders. The next definition of PCOS was formulated after the consensus opinion of experts for PCOS, held in May 2003 at Rotterdam. As per the Rotterdam European society of human reproduction and embryology (ESHRE), American society of reproductive medicine (ASRM) 2003 criteria, the diagnosis of PCOS requires the presence of two of the following three findings to be present as follows: signs of clinical or biochemical HA, chronic ovulatory dysfunction (OD) and PCOM, after ruling out other secondary causes.^[4]

Later in 2006, the AE-PCOS conducted a systematic review to study different phenotypes of PCOS. They concluded that HA is the main underlying disorder in PCOS, and this syndrome should be diagnosed based upon the presence of clinical or biochemical HA along with ovarian dysfunction (i.e., OD or PCOM), but only after ruling out other causes of androgen excess.^[5,6]

NIH conducted an Evidence-Based PCOS Workshop in the year 2012, which focused on the pros and cons of existing diagnostic criteria. They suggested the use of the initial ESHRE/ASRM 2003 criteria, but incorporated these PCOS sub-phenotypes classified as follows ^[7]:

• Phenotype A: HA (clinical or biochemical) + OD + PCOM

• Phenotype B: HA + OD

• Phenotype C: HA + PCOM; and

• Phenotype D: OD + PCOM.

Current ESHRE 2023 Guidelines summary: Diagnosis of PCOS should be done as per the revised Rotterdam criteria, which have now been modified to an evidence-based criterion. For diagnosing PCOS in adult women, any two of the following characteristics must be included: (i) clinical/biochemical features of androgen excess, (ii) OD and (iii) presence of polycystic ovaries on ultrasound or raised serum AMH levels, after excluding other important causes of HA. In those women where menstrual cycle irregularities and HA co-exist, characteristic ultrasound features of the ovaries or doing a serum test for AMH levels are not necessary for further diagnosis. In adolescents, both HA and OD must be present for the diagnosis of PCOS. However, features of PCOM on ultrasound or serum AMH levels are not recommended in adolescents due to their poor specificity.^[8]

As per the original Rotterdam consensus criteria of 2003, the definition of polycystic ovaries included ≥12 follicles in ovaries with a size of 2–9 mm and/or an ovarian volume (OV) >10 cc in at least one ovary. This ultrasound criterion to diagnose PCOM in adults has been revised in the *ESHRE guideline 2023 and includes the following: the follicle number per ovary (FNPO), the follicle number per cross-section (FNPS), and OV. According to *ESHRE guideline 2023, the most reliable ultrasound marker for identifying PCOM in adults is FNPO. A threshold of FNPO ≥ 20 in at least one ovary is now recognised for diagnosing PCOM in adults.^[8] Wherever feasible, the transvaginal approach (with 8 MHz probe frequency) is most accurate for making a diagnosis of PCOM. If older imaging technology is utilised or if the image quality does not allow for precise evaluation of follicular counts, a volume of ovary more than or equal to 10 ml or FNPS ≥ 10 in at least one ovary can still be utilised to define PCOM. Transabdominal ultrasonography (USG) should also report OV or FNPS.

They have also recommended that raised serum AMH levels can be used to define PCOM in reproductive-age women. Serum AMH can be used in patients having either irregular menstrual cycles or HA for diagnosing PCOS. But the use of serum AMH as the only diagnostic test for PCOS cannot be recommended.

AMH AND ITS ROLE IN DIAGNOSING PCOS

AMH is a dimeric glycoprotein and is a part of the transforming growth factor beta family of growth and differentiation factors.^[9] AMH is produced by granulosa cells of the ovary, located in preantral to small antral follicles (≤4–6 mm), and this synthesis is critical for follicle-stimulating hormone (FSH)-dependent folliculogenesis. The primordial follicles, dominant follicles, and atretic follicles show reduced expression of AMH. In females, AMH levels are not detectable at birth; they increase gradually until puberty, after which they remain almost static during the early reproductive years. AMH levels start declining after the age of 30 years and become very low just before menopause.^[10,11]

AMH serves to inhibit the recruitment and development of follicles, thereby resulting in the arrest of follicular growth. Through its paracrine effect, it inhibits the selection of the dominant follicle from a group of small antral follicles during the course of the gonadotropin-stimulated cycle.^[10,12]

The aromatase enzyme, essential for the production of oestrogens from androgens within granulosa cells, is downregulated by AMH until follicular selection. Expression of AMH remains elevated until a follicle becomes approximately 8 mm in size. As the size of the antral follicle increases, AMH concentration within the antral follicle progressively decreases, followed by a sharp decline once the follicle size exceeds 8 mm.^[11]

This sharp reduction in AMH coincides with the selection of the dominant follicle. Once the dominant follicle is selected, due to a decrease in AMH activity, there is increased expression of the aromatase enzyme in granulosa cells, resulting in higher oestrogen production. Thus, AMH functions as a controller of follicular selection and oestrogen production.

The serum AMH concentration can be regarded as an effective biochemical indicator of the antral follicle pool during the early follicular phase of the menstrual cycle.^[13–15] Consequently, a low count of antral follicles may lead to reduced serum AMH levels.

CONCLUSION

Serum AMH level is notably raised in women with PCOS as compared to healthy subjects and is no doubt a valuable diagnostic indicator for PCOS and correlates well with the diagnosis of PCOM on ultrasound. AMH level can help diagnose PCOS, especially if transvaginal ultrasound is not feasible and there is difficulty in assessing the ovaries during transabdominal scans. The establishment of a specific cut-off for serum AMH levels is challenging, as it is multifactorial, and, as per current evidence, the serum AMH levels cannot be relied upon as the only diagnostic criterion for PCOS. Instead, it can be used as an alternative marker of PCOM along with other Rotterdam criteria in diagnosing PCOS. In the future, with the improvement of standards and betterment of assays, the role of AMH as a surrogate marker for diagnosing PCOS will become more evident.