What Is Corpus Luteum? Why Does a Corpus Luteum Cyst Appear?

During each menstrual cycle, an ovarian follicle grows under the influence of FSH (follicle-stimulating hormone). When the follicle reaches approximately 15–20 mm, it ruptures and releases the egg. After ovulation, the egg travels into the fallopian tubes, while the follicle normally dissolves on its own if pregnancy does not occur.

However, when pregnancy does occur, the follicle transforms into the corpus luteum, a temporary but essential structure responsible for producing the hormone progesterone during early pregnancy. This hormone supports embryo implantation and helps maintain the uterine lining until placental hormone production begins around the 10th week of pregnancy.

In some cases, whether pregnancy occurs or not, the follicle does not regress as expected. Instead, fluid accumulates inside the tissue, resulting in a corpus luteum cyst. These cysts may cause pelvic pain, discomfort, or abnormal vaginal bleeding. Before explaining why cysts occur, it is important to understand what the corpus luteum is and how it functions in the menstrual cycle and early pregnancy.

What Is Corpus Luteum?

Each month, a mature egg emerges from its follicle and enters the fallopian tubes, where fertilization may take place. After the egg is released, the ruptured follicle becomes the corpus luteum, which secretes progesterone to support early pregnancy.

Functions of the corpus luteum include:

• Preparing the uterus for embryo implantation
• Thickening the uterine lining
• Increasing blood flow and oxygenation
• Preventing uterine contractions
• Supporting the embryo until the placenta takes over progesterone production

If pregnancy occurs, the corpus luteum continues its hormonal role for roughly 7–9 weeks before shrinking into a structure called the corpus albicans.

If pregnancy does not occur, the corpus luteum naturally disintegrates. However, when fluid accumulates inside this tissue, a corpus luteum cyst may form. Most cysts resolve on their own, though cysts measuring 5–7 cm may require surgical treatment.

What Is a Corpus Luteum Cyst and How Is It Diagnosed?

Under normal conditions, the corpus luteum shrinks after progesterone production shifts to the placenta or after menstruation begins. When the body fails to eliminate this fluid-filled sac, it becomes a corpus luteum cyst, also known medically as corpus hemorrhagicum.

Common symptoms of a corpus luteum cyst include:

• Pelvic pain or pressure
• Bloating or abdominal fullness
• Lower back pain
• Breast tenderness
• Painful menstruation
• Abnormal vaginal bleeding
• Pain during intercourse
• Frequent urination or difficulty urinating
• Constipation or discomfort during bowel movements

In severe cases, a cyst may enlarge, rupture, or cause internal bleeding. It may also result in ovarian torsion, a serious condition where the ovary twists and blood flow becomes restricted.

Diagnosis typically includes:

• Pelvic examination
• Pelvic ultrasound
• Hormonal blood tests

These methods help evaluate the size, structure, and potential complications of the cyst.

What Causes a Corpus Luteum Cyst?

A corpus luteum cyst forms when the follicle does not shrink and continues to accumulate fluid. Contributing factors include:

1. Failure of the follicle to regress after ovulation

The fluid-filled sac persists even after the egg has been released.

2. Fluid accumulation during early pregnancy

Even after the placenta begins producing progesterone, the corpus luteum may fail to shrink.

3. Hormonal fluctuations

Irregular hormone levels can delay the breakdown of the corpus luteum.

4. Minor bleeding into the corpus luteum

This may cause the structure to expand and form a cyst.

These factors explain why corpus luteum cysts may occur even in normal reproductive cycles.

What Does the Corpus Luteum Do During Pregnancy?

The corpus luteum plays an indispensable role in the first trimester of pregnancy. Its responsibilities include:

• Producing progesterone before the placenta develops
• Preparing the uterus for implantation
• Thickening the uterine lining
• Supporting early embryo development
• Preventing uterine contractions

If the egg is not fertilized, progesterone levels fall, the uterine lining sheds, and menstruation begins.

A corpus luteum cyst during pregnancy is typically harmless. Most do not affect fetal development. Only cysts that grow excessively or rupture may require medical monitoring or surgical removal.

How Is a Corpus Luteum Cyst Treated?

Most corpus luteum cysts are benign and resolve without treatment. Management depends on:

• The cyst’s size

• • The presence or severity of symptoms
  • Patient age

• Pregnancy status

Observation

If the cyst is small and asymptomatic, doctors usually recommend monitoring with periodic ultrasounds.

Surgical Removal

Cysts that enlarge beyond 5–7 cm, cause severe symptoms, or create complications may require laparoscopic surgery, a minimally invasive technique performed through small abdominal incisions. This approach offers:

• Faster recovery
• Reduced pain
• Low complication risk

As with other ovarian cysts, recurrence is possible.

FAQ – Frequently Asked Questions

Does a corpus luteum cyst affect pregnancy?

Most corpus luteum cysts do not interfere with pregnancy and resolve spontaneously.

Can a corpus luteum cyst rupture?

Yes. A ruptured cyst may cause internal bleeding and requires immediate medical evaluation.

Are corpus luteum cysts dangerous?

They are typically benign, but complications such as ovarian torsion or rupture can be serious.

Can a corpus luteum cyst prevent pregnancy?

Rarely. Most cysts do not affect fertility unless they become significantly large.

How do I know if I have a corpus luteum cyst?

Symptoms such as pelvic pain, fullness, or abnormal bleeding may indicate a cyst, and diagnosis is confirmed with ultrasound.

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