Sonographic Classification of Ovulation Disorders (Hilgers Classification)

By RRM Academy Reviewed by Dr. Naomi Whittaker, MD, Board-Certified OBGYN, MIGS, NFPMC, FCI Updated May 14, 2026

Sonographic ovulation classification is a serial transvaginal ultrasound framework, developed within NaProTechnology practice, that characterizes the quality of the periovulatory event and distinguishes anatomically normal ovulation from six distinct pathological patterns and one anovulatory variant.

An LH surge confirms that the ovulatory signal fired. It does not confirm that the follicle was mature, ruptured fully, released the oocyte intact, or formed a structurally adequate corpus luteum. Serial periovulatory ultrasound captures what actually occurred at the follicle after the LH surge.¹

Normal ovulation requires a dominant follicle reaching adequate mean diameter at rupture, a positive cumulus oophorus sign confirming oocyte-cumulus complex release, and complete follicle collapse. Deviation from any criterion defines a specific disorder category. The classification identifies eight patterns: anatomically normal ovulation; Luteinized Unruptured Follicle Syndrome (LUF), in which the follicle luteinizes without releasing the oocyte; Immature Follicle Syndrome, in which the follicle ruptures before reaching adequate size; Partial Rupture Syndrome, in which follicle collapse is incomplete over the expected timeframe; Delayed Rupture Syndrome, in which rupture occurs but is spread across an abnormally prolonged window; mature follicle with absent or retained cumulus oophorus; Afollicularism, in which no follicle reaches dominance; and Empty Follicle Syndrome, in which the cumulus oophorus sign is absent despite apparent follicle development.

Each pattern carries distinct implications for fertility and maps to a specific mechanism. LUF produces an apparent luteal phase with no oocyte available for fertilization. Immature follicle rupture reduces oocyte quality and corpus luteum progesterone output. Partial and delayed rupture affect gamete release and may produce pelvic adhesions over time. Afollicularism and empty follicle syndrome represent the most severe end of the spectrum, overlapping with anovulatory cycle physiology.

A follicle maturation study is the ultrasound series that generates this classification. Classification drives intervention: different ovulatory disorders have different root causes, and identifying the precise pattern is the first step toward addressing it.

This content is for educational purposes only and does not constitute medical advice. Consult an RRM clinician or healthcare provider for guidance specific to your situation.