Classification of Human Ovarian Follicle Morphology: Recommendations of the NICHD-Sponsored Ovarian Nomenclature Workshop.

Objective: To develop a consensus on histologic human ovarian follicle staging nomenclature, provide guidelines for follicle density calculation, and assess changes due to fixation to enhance communication among clinicians and ovarian biology researchers in order to gain a deeper understanding of human fertility.

Methods: Beginning in March 2021, the Ovarian Nomenclature Workshop's Follicle Classification Working Subgroup was organized by the Pediatric and Adolescent Gynecology program of the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD).

Results: The Follicle Working Subgroup recommends consolidation and expansion of the current classification systems to include six stages of normal preantral follicles, five stages of normal antral follicles, as well as categories of corpus lutea, abnormal preantral follicles, abnormal antral follicles, and other distinct follicle types. The new preantral staging added intermediate stages (primordial, transitional primordial, primary, transitional primary, secondary, multilayer ovarian follicles). The antral follicle staging includes: early pre-selection, selection, dominance, and pre-ovulatory follicles. Abnormal preantral follicles include those with an abnormal oocyte (AMF-o), granulosa cells (AMF-g), or both (AMF-og). We suggest a uniform way of calculating mean follicle density in number of follicles/mm².

Conclusion: To establish a consensus in ovarian follicle terminology, the Ovarian Follicle Working Subgroup of the NICHD Ovarian Nomenclature Workshop standardized Follicle Staging Nomenclature and Follicle Density Calculating Systems so consistent common language can be used among ovarian biology researchers and clinicians.