Luteinized Unruptured Follicle (LUF) Syndrome

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

Luteinized Unruptured Follicle (LUF) syndrome is a condition in which the dominant follicle undergoes luteinization, signaling progesterone production, without physically rupturing to release the oocyte. Ovulation appears to have occurred by hormonal parameters, and menstrual cycles typically proceed at normal intervals, yet fertilization cannot take place because the egg was never released. LUF syndrome is a clinically underappreciated contributor to infertility that goes undetected without serial ultrasound monitoring across the cycle.¹

Diagnosis requires sonographic confirmation. Serial follicle tracking documents the growth of the dominant follicle to expected mature size, followed by signs of luteinization such as increased echogenicity and structural change within the follicle wall, without the collapse and fluid release that accompanies true rupture. The follicle persists where an empty, collapsed structure would normally follow ovulation.¹

LUF syndrome may occur intermittently, not in every cycle, which adds to its diagnostic complexity. A single cycle of monitoring that captures a normal ovulation does not exclude it. Because LUF cycles produce progesterone, luteal-phase charting alone cannot distinguish them from ovulatory cycles without ultrasound. Identifying LUF syndrome converts a clinically "unexplained" infertility presentation into a diagnosable, addressable finding.

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.