Overview of the Corpus Luteum
The corpus luteum is the last active stage of an ovarian follicle’s lifecycle. Without it, early pregnancy cannot be maintained. The corpus luteum doesn’t get enough credit for the important roles in plays in pregnancy and the menstrual cycle. Here’s what you should know.
The corpus luteum forms from the empty follicle left behind after ovulation. Your ovary is made up of follicles, which are very tiny fluid-filled sacs, each containing an immature egg (or oocyte.) During the first couple weeks of your menstrual cycle, hormones regulated by the hypothalamus and released by the pituitary gland trigger a few of these follicles to grow and the egg inside the follicles to mature.
How Does the Corpus Luteum Work: In More Detail
- The follicular phase: this is when a select number of follicles in the ovary mature until one releases an egg.
- The luteal phase: this is post-ovulation when the body prepares the womb to accept a fertilized egg or embryo.
Just before ovulation, there is a surge in the hormone LH, or luteinizinghormone. This hormone is vital both for ovulation and what happens just after ovulation.
Once the egg is released, LH continues to impact the cellular structure of the former follicle. Before ovulation, granulosa and theca cells in the follicle produce estrogen. However, after ovulation, LH triggers these cells to transform. They begin to release the hormone progesterone.
Secondly, progesterone prepares the endometrium, or the uterine lining. Progesterone triggers the endometrium to secrete proteins. These proteins maintain the endometrium and create a nourishing environment for a fertilized egg (or embryo.)
What Happens to the Corpus Luteum If You Get Pregnant? Or If You Don’t?
If you get pregnant, and an embryo implants itself into the uterine lining, a very early placenta is formed by the embryo. This early placenta releases the pregnancy hormone hCG. (That’s the hormone pregnancy tests detect.)
Also, the drop in progesterone signals the pituitary and hypothalamus glands to increase production of FSH, LH, and GnRH. This restarts your menstrual cycle, and the follicular phase starts anew.
What Is the Corpus Albicans?
When the corpus luteum breaks down, scar tissue is left behind. This scar tissue—which is made up of cartilage—is known as the corpus albicans. While the corpus luteum is yellow in color (corpus luteum means yellow body in Latin), the corpus albicans is white. Corpus albicans means white body in Latin.
What Is a Corpus Luteum Cyst?
You may remember from above that the corpus luteum is formed from the broken open follicle that released an egg during ovulation. Sometimes, the opening of the corpus luteum seals back up. Fluid fills the cavity and forms a cyst. This kind of cyst is known as a functional cyst. They are usually benign (not cancerous) and go away on their own.
Some women find out they have one of these cysts during an early pregnancy ultrasound. In these cases, the cyst will usually resolve on its own by the second trimester of pregnancy. If your doctor sees the cyst is unusually large or growing, or it’s especially painful, your doctor may surgically drain or remove it.
As long as the pain is not severe and not accompanied by other worrisome symptoms (like vomiting or fever), there is probably nothing to worry about. Mention it to your doctor, but try not to worry about it too much.
In rare cases, a corpus luteum cyst can cause severe pain. In very rare cases, if the cyst grows especially large, it can cause the ovary to twist. This may lead to ovarian torsion. Surgical intervention would be required.
As always, if you’re experiencing severe pain or unusual bleeding, go to the nearest emergency room, or contact your doctor immediately. Ovarian torsion can be very serious.
What Is a Corpus Luteum Deficiency or Defect?
As you read above, the corpus luteum is responsible for producing the hormone progesterone. In some cases, the corpus luteum doesn’t produce enough progesterone. This can lead to abnormal spotting. Low levels of progesterone may lead to a “light period,” making you think you’re not pregnant when you really are.
However, there’s no current evidence that these treatments help. Also, hCG increases the risk of developing ovarian hyperstimulation syndrome (OHSS). Proper diagnosis of a corpus luteum defect is also controversial and unclear. Based on the current evidence, the American Society for Reproductive Medicine doesn’t recognize luteal phase defect as a specific cause of infertility.