The corpus luteum is a temporary hormone-producing structure that forms on your ovary after you ovulate each month. It develops from the empty follicle that just released an egg, and its primary job is to pump out progesterone, the hormone that prepares the uterine lining for a potential pregnancy. If pregnancy doesn’t occur, the corpus luteum breaks down about 10 days after ovulation, triggering your period.
How the Corpus Luteum Forms
Each month during your menstrual cycle, a follicle in one of your ovaries matures and eventually ruptures to release an egg. That rupture is ovulation. What’s left behind isn’t discarded. Instead, the collapsed follicle undergoes a rapid transformation. The cells that previously surrounded the egg change their behavior, growing and filling with yellow pigment (the name “corpus luteum” is Latin for “yellow body”). Blood vessels quickly grow into the new structure, giving it one of the richest blood supplies of any tissue in the body.
This transformation is triggered by a surge of luteinizing hormone (LH) from the pituitary gland. LH doesn’t just cause ovulation; it also reprograms the leftover follicle cells into a progesterone-producing factory. Two types of cells make up the corpus luteum, each with a different origin: one type comes from the inner lining of the follicle, and the other from the outer layer. The outer-origin cells respond directly to LH by ramping up progesterone production.
What the Corpus Luteum Does
The corpus luteum’s main product is progesterone, with smaller amounts of estrogen. Progesterone does the critical work of transforming the uterine lining into a nutrient-rich environment where a fertilized egg could implant and grow. Without adequate progesterone during this phase, the lining can’t support a pregnancy.
Progesterone levels aren’t steady. They pulse in response to LH signals, fluctuating between roughly 5 and 40 ng/mL over short periods in women who are ovulating normally. A blood level above 3 ng/mL is generally considered confirmation that ovulation has occurred. For the uterine lining to develop normally at the cellular level, progesterone needs to reach a peak somewhere between 8 and 18 ng/mL.
Beyond preparing the uterus, progesterone from the corpus luteum also causes the slight rise in basal body temperature that many people track when monitoring fertility. It’s responsible for many of the physical sensations in the second half of the cycle: breast tenderness, mild bloating, and changes in mood.
Its Role in Early Pregnancy
If a fertilized egg implants in the uterine lining, the developing embryo starts producing a hormone called hCG (the same hormone detected by pregnancy tests). hCG sends a rescue signal to the corpus luteum, preventing it from breaking down. As long as hCG keeps arriving, the corpus luteum continues producing the progesterone that the pregnancy depends on.
This arrangement is temporary. Around 7 weeks of gestation, the placenta begins producing enough progesterone on its own to sustain the pregnancy. By about 8 to 9 weeks, the placenta has largely taken over. This transition is sometimes called the luteal-placental shift. After that point, the corpus luteum becomes less critical, though it doesn’t disappear entirely until later in pregnancy.
What Happens Without Pregnancy
In a cycle where pregnancy doesn’t occur, no hCG arrives to sustain the corpus luteum. Without that signal, the structure begins to deteriorate about 10 days after ovulation. Its functional lifespan is roughly 14 days, give or take two.
The breakdown process, called luteolysis, involves several factors. Prostaglandins and estrogen both appear to play a role in triggering the decline, and immune cells, specifically white blood cells and macrophages, progressively infiltrate the structure. Without the support of LH or hCG, the cells undergo programmed cell death.
As progesterone levels drop, the uterine lining loses its hormonal support and sheds. That’s your period. Meanwhile, the remnants of the corpus luteum gradually fill with scar tissue and shrink into a small white structure called the corpus albicans (Latin for “white body”). This scar can persist in the ovary for several cycles before fully disappearing.
Corpus Luteum Cysts
Sometimes the corpus luteum fills with fluid and forms a cyst. A corpus luteum cyst is typically between 1 and 3 centimeters and is considered a normal, harmless, functional cyst. Most resolve on their own within a few weeks without treatment.
These cysts can occasionally cause a dull ache on one side of the lower abdomen. In rare cases, a larger cyst can rupture or twist the ovary, which causes sudden, sharp pain and may need medical attention. But the vast majority go unnoticed. Many are discovered incidentally on ultrasounds performed for other reasons.
Luteal Phase Deficiency
When the corpus luteum doesn’t produce enough progesterone, or doesn’t produce it for long enough, the result is a condition called luteal phase deficiency. The uterine lining never fully matures, making implantation difficult and potentially contributing to infertility or early pregnancy loss.
Diagnosing this condition is tricky because progesterone levels fluctuate so much throughout the day. A single blood draw might catch a peak or a trough, making any one reading unreliable. The underlying problem usually traces back to the first half of the cycle: if the follicle doesn’t develop properly before ovulation, the corpus luteum that forms from it won’t function well either. Poor follicle development, inadequate LH signaling, or disruptions in ovulation can all lead to a weak corpus luteum and insufficient progesterone in the second half of the cycle.