A corpus luteum is a mass of cells that forms in an ovary. It is a temporary organ that appears every menstrual cycle and disappears if fertilization does not occur. It also produces the hormone progesterone during early pregnancy.

The role of the corpus luteum depends on whether or not fertilization occurs.

Sometimes, cysts can form in a corpus luteum, leading to painful symptoms. These cysts can go away on their own, but some may require treatment.

This article examines the role of the corpus luteum and how it forms. It also takes a look at what happens when corpus luteum cysts form and what how to treat them.

A note about sex and gender

Sex and gender exist on spectrums. This article will use the terms “male,” “female,” or both to refer to sex assigned at birth. Click here to learn more.

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During ovulation, an egg is released from a dominant follicle. Following the release of the egg and subsequent fertilization, the follicle seals itself off and forms what is known as a corpus luteum. This mass of cells helps produce the hormone progesterone during early pregnancy.

The corpus luteum will continue to produce progesterone until the fetus produces adequate levels to sustain the pregnancy, which usually occurs within weeks 7-9 of pregnancy.

Progesterone is essential during early pregnancy because:

  • It allows the uterus to grow without having contractions.
  • It supports the growth of the lining of the uterus.
  • It improves blood flow and oxygen supply.

The pregnancy hormone human chorionic gonadotropin (hCG) supports and maintains the corpus luteum. The corpus luteum begins to decrease in size at around 10 weeks of pregnancy.

When fertilization or implantation does not occur, the corpus luteum will begin to break down. This causes a decline in estrogen and progesterone levels, leading to the start of another menstrual period.

Hormones play a powerful role in typical menstrual regulation in females.

In addition to progesterone and estrogen, essential hormones for ovulation include luteinizing and follicle-stimulating hormone. These hormones are responsible for ovulation and the preparation of the uterus for the implantation of a fertilized egg.

A typical menstrual cycle occurs every 25–30 days, at which time the body prepares for ovulation and pregnancy.

There are three phases of the menstrual cycle:

Follicular phase

The follicular phase of the menstrual cycle begins on the first day of a person’s period, at the onset of menstrual bleeding, and lasts until ovulation. This stage typically lasts about 13–14 days.

During the follicular phase, the body secretes follicle-stimulating hormones to induce the production of ovarian follicles that contain eggs. One of these follicles will grow into a mature follicle capable of being fertilized, which is known as the dominant follicle.

The dominant follicle secretes estrogen, which breaks down the non-dominant follicles and stimulates the uterus to begin thickening its lining in preparation for egg implantation. It also causes the luteinizing hormone surge responsible for ovulation.

Ovulatory phase

The ovulatory phase begins on approximately day 14 of the menstrual cycle. During this time, the luteinizing hormone surges, further stimulating the ovary to release the egg from the dominant follicle.

Typically, this phase lasts around 16–32 hours, resulting in ovulation.

Luteal phase

The body prepares for the implantation of a fertilized egg during the luteal phase of the menstrual cycle. When an ovarian follicle releases an egg during the ovulatory phase, the opened follicle closes off, forming what is called the corpus luteum.

The corpus luteum is responsible for producing the hormone progesterone, which stimulates the uterus to thicken even more in preparation for the implantation of a fertilized egg.

The hormone estrogen also increases during this time to prepare the uterus for implantation.

If there are no fertilized eggs to implant in the thickened uterine lining, the body sheds the lining during menstrual bleeding due to low levels of estrogen and progesterone, and the cycle begins again.

A corpus luteum defect, also known as a luteal phase defect, occurs when the corpus luteum is unable to produce enough progesterone to prepare the endometrium for implantation and pregnancy.

This can cause issues like infertility and miscarriage.

According to the American Society for Reproductive Medicine, factors and health conditions that may interfere with the function of the corpus luteum include:

Treatment for a corpus luteum defect may vary depending on the cause but often involves progesterone supplementation to support fertility.

At times, the corpus luteum can fill with fluid. This buildup causes what is called a corpus luteum cyst, which is a type of functional ovarian cyst.

In most cases, corpus luteum cysts will go away on their own without treatment. Corpus luteum cysts may disappear in a few weeks or take up to three menstrual cycles to vanish altogether.

Some people who develop these cysts may experience symptoms, such as:

  • pelvic pain, which may present as dull or sharp aching
  • abdominal fullness or heaviness
  • bloating
  • aching in the lower back and thighs
  • painful intercourse
  • weight gain
  • painful menstrual bleeding
  • breast tenderness
  • need to urinate more frequently
  • difficulty emptying the bladder
  • difficulty emptying bowels completely
  • abnormal vaginal bleeding

Some people may experience a burst cyst, which can cause severe pain and possibly internal bleeding.

Larger cysts can cause the ovary to twist on itself (ovarian torsion). This can negatively affect the blood flow to the affected ovary.

At times, the corpus luteum cyst may remain past the early stages of pregnancy. If this happens, the cyst has the potential to cause problems. An obstetrician will monitor as appropriate and make referrals to specialists as necessary.

A doctor may feel some ovarian cysts during a pelvic exam, but not always.

An obstetrician may carry out some diagnostic tests to evaluate and diagnose ovarian cysts, including:

  • a pregnancy test, which may signal the presence of a corpus luteum cyst
  • hormone testing
  • pelvic ultrasound
  • surgical procedures, such as laparoscopy, where the doctor inserts an instrument into the uterus through a small cut in her abdomen

Some doctors may carry out tests to check the levels of certain substances in the blood used to detect ovarian cancer, such as the cancer antigen 125 (CA 125) test.

A doctor would most likely request these tests if the cyst is solid and the person is at a higher risk for ovarian cancer. However, CA 125 levels can also rise in noncancerous conditions such as endometriosis.

Often, corpus luteum cysts resolve without treatment. However, there are times when treatment is necessary.

Some treatment options for ovarian cysts include:

A doctor will decide whether treatment is needed based on the size of the cyst, the symptoms that it may be causing, and the person’s age.

If a cyst is not causing any symptoms, the doctor will often wait to see how things progress rather than starting any form of treatment.

Here are a few common questions about the corpus luteum.

What does the corpus luteum do if not pregnant?

If a person does not get pregnant during the menstrual cycle, the body breaks down the corpus luteum. This leads to a decline in hormone levels.

What does the presence of corpus luteum mean?

The corpus luteum is a mass of cells that forms in the ovaries each month during a person’s menstrual cycle. It is responsible for producing key hormones involved in reproductive health and fertility, including progesterone.

Do corpus luteum cysts need to be removed?

A corpus luteum cyst does not usually require treatment and often resolves on its own over time. However, a doctor may recommend treatment in some cases, depending on a person’s symptoms, medical history, age, and the size of the cyst.

The corpus luteum helps produce hormones that the body needs during the early stages of pregnancy. It is a vital part of fertility that enables pregnancy to occur.

Cysts can sometimes form if the corpus luteum fills up with fluid. If anyone experiences any of the symptoms associated with a corpus luteum cyst, they should speak to a doctor.

These cysts can cause painful symptoms, but in most cases, they will go away in time without treatment.