A new comprehensive ovulatory disorders classification system developed by FIGO
Munro MG, Balen AH, Cho S, et al; FIGO Committee on Menstrual Disorders and Related Health Impacts, and FIGO Committee on Reproductive Medicine, Endocrinology, and Infertility. The FIGO ovulatory disorders classification system. Fertil Steril. 2022;118:768-786.
Ovulatory disorders are well-recognized and common causes of infertility and abnormal uterine bleeding (AUB). Ovulatory disorders occur on a spectrum, with the most severe form being anovulation, and comprise a heterogeneous group that has been classically categorized based on an initial monograph published by the World Health Organization (WHO) in 1973. That classification was based on gonadotropin levels and categorized these disorders into 3 groups: 1) hypogonadotropic (such as hypothalamic amenorrhea), 2) eugonadotropic (such as polycystic ovary syndrome [PCOS]), and 3) hypergonadotropic (such as primary ovarian insufficiency). This initial classification was the subject of several subsequent iterations and modifications over the past 50 years; for example, at one point, ovulatory disorder caused by hyperprolactinemia was added as a separate fourth category. However, due to advances in endocrine assays, imaging technology, and genetics, our understanding of ovulatory disorders has expanded remarkably over the past several decades.
Previous FIGO classifications
Considering the emergent complexity of these disorders and the limitations of the original WHO classification to capture these subtleties adequately, the International Federation of Gynecology and Obstetrics (FIGO) recently developed and published a new classification system for ovulatory disorders.5 This new system was designed using a meticulously followed Delphi process with inputs from a diverse group of national and international professional organizations, subspecialty societies, specialty journals, recognized experts in the field, and lay individuals interested in the subject matter.
Of note, FIGO had previously published classification systems for nongestational normal and abnormal uterine bleeding in the reproductive years (FIGO AUB System 1),as well as a subsequent classification system that described potential causes of AUB symptoms (FIGO AUB System 2), with the 9 categories arranged under the acronym PALM-COEIN (Polyp, Adenomyosis, Leiomyoma, Malignancy–Coagulopathy, Ovulatory dysfunction, Endometrial disorders, Iatrogenic, and Not otherwise classified). This new FIGO classification of ovulatory disorders can be viewed as a continuation of the previous initiatives and aims to further categorize the subgroup of AUB-O (AUB with ovulatory disorders). However, it is important to recognize that while most ovulatory disorders manifest with the symptoms of AUB, the absence of AUB symptoms does not necessarily preclude ovulatory disorders.
New system uses a 3-tier approach
The new FIGO classification system for ovulatory disorders has adopted a 3-tier system.
The first tier is based on the anatomic components of the hypothalamic-pituitary-ovarian (HPO) axis and is referred to with the acronym HyPO, for Hypothalamic-Pituitary-Ovarian. Recognizing that PCOS refers to a distinct spectrum of conditions that share a variable combination of signs and symptoms caused to varying degrees by different pathophysiologic mechanisms that involve inherent ovarian follicular dysfunction, neuroendocrine dysfunction, insulin resistance, and androgen excess, it is categorized in a separate class of its own in the first tier, referred to with the letter P.
Adding PCOS to the anatomical categories referred to by HyPO, the first tier is overall referred to with the acronym HyPO-P (FIGURE 2).5
The second tier of stratification provides further etiologic details for any of the primary 3 anatomic classifications of hypothalamic, pituitary, and ovarian. These etiologies are arranged in 10 distinct groups under the mnemonic GAIN-FIT-PIE, which stands for Genetic, Autoimmune, Iatrogenic, Neoplasm; Functional, Infectious/inflammatory, Trauma and vascular; and Physiological, Idiopathic, Endocrine.
The third tier of the system refers to the specific clinical diagnosis. For example, an individual with Kallmann syndrome would be categorized as having type I (hypothalamic), Genetic, Kallmann syndrome, and an individual with PCOS would be categorized simply as having type IV, PCOS.
WHAT THIS EVIDENCE MEANS FOR PRACTICE
Our understanding of the etiology of ovulatory disorders has substantially increased over the past several decades. This progress has prompted the need to develop a more comprehensive classification system for these disorders. FIGO recently published a 3-tier classification system for ovulatory disorders that can be remembered with 2 mnemonics: HyPO-P and GAIN-FIT-PIE.
It is hoped that widespread adoption of this new classification system results in better and more concise communication between clinicians, researchers, and patients, ultimately leading to continued improvement in our understanding of the pathophysiology and management of ovulatory disorders.
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