Luteinized unruptured follicle syndrome (LUFS) is a form of anovulation in which ovulation does not occur successfully. LUFS is also known as "trapped egg syndrome". In LUFS, the egg matures fully or partially inside the ovary but is never released. This occurs when the dominant egg follicle does not rupture, and the cells left behind in the eggs follicle undergo a hormonal change called luteinization and produce progesterone, the hormone that prepares and maintains the uterine lining for implantation. As a result of the increased progesterone secretion, the uterine lining develops its normal characteristic changes following ovulation, but no oocyte is released, and conception cannot occur. LUFS is a rare condition. It occurs in more than 50% of women with unexplained infertility and is also more frequent in women with endometriosis.

LUFS can be treated with medication in some cases. The use of either hCG alone or hCG in combination with hMG in a single injection at the time of follicular maturation successfully corrected mature follicle LUF in 21 of 46 patients (46%) . Ovulation-inducing drugs plus hCG or hCG and hMG corrected LUF in 24 of 25 patients (96%) . Clomiphene citrate proved inferior to hMG in that it corrected LUF in 3 of 25 patients (12%) versus 12 of 22 patients (95%) who had.

In conclusion, LUFS is a condition where the dominant egg follicle does not rupture, and the egg is not released. It is a rare condition that can be treated with medication in some cases. LUFS is more frequent in women with endometriosis and occurs in more than 50% of women with unexplained infertility.