Corpus Luteum

After a follicle releases its egg at ovulation, the remaining follicular cells transform into the corpus luteum (Latin for "yellow body"). Under the influence of LH, the corpus luteum secretes progesterone — and some estradiol — for approximately 14 days in a non-conception cycle, after which it degenerates (luteolysis) and progesterone falls, triggering menstruation.

If pregnancy occurs, hCG from the implanting embryo rescues the corpus luteum, prolonging progesterone production until the placenta takes over around 8–10 weeks. In IVF, since stimulation protocols suppress LH, the corpus luteum may be inadequate, which is why exogenous progesterone supplementation is standard. A corpus luteum cyst is a fluid-filled structure that sometimes forms and is usually benign and self-resolving.