The corpus luteum

The corpus luteum is an endocrine glandular structure which (also) has the function of producing progesterone. It is the last active stage of the life cycle of an ovarian follicle. If there is no corpus luteum, it is not possible to establish and maintain a pregnancy, therefore it is important to understand the importance of this stage and its extremely important role for both pregnancy and the menstrual cycle.

The corpus luteum forms from the follicle that has emptied following ovulation. The ovary is made up of follicles, which are very small sacs of fluid, each containing an immature egg (called an oocyte).

During the first few weeks of the menstrual cycle, hormones regulated by the hypothalamus are released into the pituitary gland and stimulate some of these follicles to grow, as the egg they contain matures. Eventually, one of these follicles becomes dominant and from this the egg will be released during ovulation.

The egg is released as the follicle bursts, leaving behind an empty shell of cells. These, following the release of the egg, collapse on themselves and undergo a change in the hormones they produce, forming the corpus luteum.

It could be said that the corpus luteum is a temporary glandular structure, which secretes the hormones estrogen and progesterone, preparing the body for an eventual conception. These are in fact the hormones that serve to make the inner lining of the uterus grow so that it is hospitable for the implantation of the egg and so that it is maintained over time.

If conception does not occur, the corpus luteum begins to fall apart causing a drop in progesterone and estrogen, which causes menstruation, starting the cycle again from the beginning. When the corpus luteum is no longer active, it transforms into the corpus albicans .

How the corpus luteum works

To understand how the corpus luteum works, one must understand what happens during ovulation. There are two main phases in the menstrual cycle:

  • the follicular phase : a small number of follicles mature in the ovary until one of them releases an egg.
  • the luteal (or luteal) phase : the one in which – after ovulation – the body prepares to welcome the fertilized egg or embryo.

Just prior to ovulation , there is a surge of luteinizing hormone or LH, which is very important for both ovulation and its aftermath.

In fact, before ovulation, LH stimulates the follicle and the maturing egg to accelerate development. It also stimulates the production of enzymes that begin to break down the outer walls of the follicle. Eventually, the egg will finish maturing and the follicle will rupture open. The release of the mature egg is called ovulation. Once the egg is released, the luteinizing hormone continues to affect the cellular structure of the follicle.

Before ovulation, the theca and granulosa cells produce estrogen in the follicle. However, after ovulation, these cells transform and begin to release progesterone. Progesterone plays an important role in the luteal phase.

  • First, progesterone signals the pituitary gland and hypothalamus to decrease production of the hormones FSH, LH and GnRH, preventing the maturation of other follicles in the ovary and therefore ovulation again.
  • In addition, progesterone causes the endometrium, the inner lining of the uterus, to mature so that it can accommodate the fertilized egg.
  • Another function of progesterone is to signal the breast to prepare for milk production. Because of this, your breasts may be more swollen after ovulation and before your period.

What happens to the corpus luteum if you get pregnant, or if you don’t get pregnant

If you become pregnant and the embryo implants itself in the uterine lining, a very primordial placenta is formed from the embryo. This begins to produce the hormone hCG ( chorionic gonadotropin ), as well as the hormone detected by pregnancy tests .

The hCG signals the corpus luteum to continue producing progesterone. Progesterone is needed to prevent the endometrium from breaking down, which causes the egg to be expelled and continues to prevent ovulation again.

However, if a pregnancy does not occur, the corpus luteum disintegrates, approximately 10-12 days after ovulation or 2-3 days before menstruation.
When the corpus luteum breaks down, its cells stop producing progesterone, which causes the endometrium to flake and menstruation to begin. Furthermore, the drop in progesterone signals the pituitary gland and hypothalamus to increase the production of FSH, LH and GnRH again, thus causing a new menstrual cycle and a new follicular phase.

What is it, and what function does the corpus albicans have ?

When the corpus luteum ruptures, it leaves behind scar tissue, made up of cartilage, called the corpus albicans . While the corpus luteum is yellow (as the Latin name suggests), the corpus albicans is white.

The corpus albicans remains in the ovary for a few months until it too ruptures. It does not appear to have any particular function and does not appear to produce any hormones.
In the end what happens to the corpus albicans ? Immune cells called macrophages act as scavengers and engulf most of the cells that were once part of the corpus albicans. In rare circumstances, the corpus albicans remains as scar tissue that extends into the ovary.

What is a corpus luteum cyst?

As mentioned above, the corpus luteum is formed from the open follicle that has ruptured following ovulation. Sometimes this opening is closed, fluid fills the cavity and forms a cyst. This type of cyst is called functional, is usually benign (non-cancerous) and goes away on its own.

If you are undergoing fertility treatments, it is possible that a cyst of this type will be detected by ultrasound early in the period. Depending on the size of the cyst, your doctor may decide to delay treatment or treat the cyst.

If you are naturally prone to develop corpus luteum cysts, your doctor may decide to prescribe birth control pills before treatment, so as to prevent ovulation that month, thus preventing the formation of another corpus luteum and therefore a potential cyst. Cysts are usually painless and harmless.

Some women discover they have a cyst during their first ultrasound scans in early pregnancy . In these cases, the cysts usually resolve on their own in the second trimester . If your doctor thinks your cyst is too large or growing, or if it is too large, they may decide to remove it. ( 3 )

Pain due to a cyst of the corpus luteum

Sometimes, a corpus luteum cyst can cause mild discomfort. It may feel like a sharp stab of pain, but quickly disappearing on one side. Other times it can cause a dull, more constant pain focused on one side of the pelvic area.

If you become pregnant, this pain may persist longer during the first few weeks of pregnancy.

If you don’t get pregnant , the pain will probably go away a few days after you start your period.

As long as the pain isn’t severe and isn’t accompanied by other, more significant symptoms (such as vomiting or fever), there’s probably nothing to worry about. Mention this to your doctor, but try not to worry too much.

In rare cases , a corpus luteum cyst can cause severe pain.

In very rare cases , if the cyst grows abnormally, it can cause the ovary to rotate. This can lead to ovarian torsion requiring surgery.

As always, if you experience severe pain or unusual bleeding, go to the nearest emergency room or contact your doctor right away. Ovarian torsion can be very serious.

What does a corpus luteum deficiency mean and what does it imply?

As you read above, the corpus luteum is responsible for producing the hormone progesterone . In some cases, the corpus luteum doesn’t make enough progesterone.

This can cause abnormal spotting. Low progesterone levels can lead to “light bleeding,” making you think you’re not pregnant when you really are.

When progesterone levels are low after ovulation, we can speak of a corpus luteum defect. Most commonly, it refers to a luteal phase defect. A deficiency in the corpus luteum can increase the risk of early miscarriage.

Treatment of this condition may include progesterone supplementation or the use of fertility drugs such as Clomid or hCG injections. The “theory” is that boosting the hormones that lead to ovulation (with fertility drugs) will help produce a stronger corpus luteum. However, there is no evidence that these treatments are really helpful. Additionally, hCG increases the risk of developing ovarian hyperstimulation syndrome (OHSS).

The correct diagnosis of a corpus luteum defect is also controversial and unclear. Based on current evidence, luteal phase defect is not recognized as a specific cause of infertility. ( 1 , 2 )

Katherine Johnson, M.D., is a board-certified obstetrician-gynecologist with clinical expertise in general obstetrics and gynecology, family planning, women’s health, and gynecology.

She is affiliated with the Obstetrics and Gynecology division at an undisclosed healthcare institution and the online platform,

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