Corpus luteum – What is it? How important is pregnancy?

The undefined corpus luteum is a temporary structure with crucial roles in ovulation and in the early stages of pregnancy in women. On closer inspection, the corpus luteum  is a yellow-tinged mass that sits on top of the female ovaries. It begins to form at the site of the “follicle” or sac after it matures and is starting the ovulation process.

Ovulation, in turn, describes the process by which a mature follicle is finally able to rupture and release an egg that can be fertilized by a sperm. This disruption, then, is what makes pregnancy possible—thus revealing the clutching role that the corpus luteum  plays in sustaining life.

What is the corpus luteum?

During your reproductive years, your body will regularly prepare for pregnancy, whether or not you are planning to become pregnant. The result of this grooming cycle is a woman’s menstrual cycle.

The menstrual cycle has two phases, the follicular phase and the post-ovulatory or luteal phase. The luteal phase lasts approximately two weeks. During this time, a corpus luteum forms in the uterus. The corpus luteum  is made up of a follicle that houses a maturing egg. It starts to form as soon as a mature egg leaves the follicle. The corpus luteum  is essential for conception and for a pregnancy to last.

During ovulation, an egg is released from a dominant follicle. After the release of the egg and subsequent fertilization, the follicle isolates itself and forms what is known as the 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 is producing adequate levels to sustain pregnancy, which usually occurs between 7 and 9 weeks of gestation. Progesterone is essential during early pregnancy because:

  1. Allows the uterus to grow without contractions;
  2. Supports the growth of the lining of the uterus;
  3. Improves blood flow and oxygen supply;
  4. The corpus luteum is supported and maintained by the pregnancy hormone, human chorionic gonadotropin or HCG. The corpus luteum  begins to decrease in size around 10 weeks of pregnancy.

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

Corpus luteum and the menstrual cycle:

Hormones play a powerful role in normal menstrual regulation in women.

As well as progesterone and estrogen , other hormones essential for ovulation include luteinizing and follicle-stimulating hormone.

These hormones are responsible for ovulation and preparing the uterus for implantation of a fertilized egg.

A typical menstrual cycle occurs every 25 to 36 days as the body prepares for ovulation and pregnancy. There are three phases of the menstrual cycle:

1. Follicular phase:

The follicular phase of the menstrual cycle begins on the first day of a woman’s period, at the beginning of menstrual bleeding, and lasts until ovulation. This stage usually lasts for 13 to 14 days.

During the follicular phase, the body secretes follicle stimulating hormone 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 not only breaks down non-dominant follicles, but also stimulates the uterus to start thickening its lining in preparation for egg implantation. It also causes the increase in luteinizing hormone which is responsible for ovulation.

2. Ovulatory phase:

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

Typically, this phase lasts from 16 to 32 hours, resulting in ovulation.

3. Luteal Phase:

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

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

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

If there are no fertilized eggs for implantation in the thick uterine lining, the body sheds the lining during menstrual bleeding due to low levels of estrogen  and progesterone, and the cycle starts all over again.

Function of the corpus luteum in pregnancy:

The main purpose of the corpus luteum is to pulse hormones, including progesterone.

Progesterone is necessary for a viable pregnancy to occur and continue. Progesterone helps the uterine lining, known as the endometrium, to thicken and become spongy. These changes in the uterus allow for the implantation of a fertilized egg.

The uterus also provides a rapidly growing embryo with nutrition during its early stages of development, until the placenta, which also produces progesterone, can take over.

If a fertilized egg does not implant in the endometrium, pregnancy does not occur. The corpus luteum  decreases and progesterone levels drop. The uterine lining then sheds as part of menstruation.

Corpus luteum defect:

It is possible to have a defect in the corpus luteum . This is also referred to as a luteal phase defect. It is caused if there is not enough progesterone in the uterus to thicken the endometrium. It can also occur if the endometrium does not thicken in response to progesterone, even though some progesterone is present.

The corpus luteum defect  can be caused by many conditions. They include:

  1. Body mass index too high or too low;
  2. Extreme amounts of exercise;
  3. Short luteal phase;
  4. Polycystic ovary syndrome (PCOS);
  5. Endometriosis;
  6. Hiperprolactinemia;
  7. Thyroid disorders, including underactive thyroid, overactive thyroid, iodine deficiency, and Hashimoto ‘s disease ;
  8. extreme stress ;
  9. Perimenopausa.

The corpus luteum defect  can also occur for unknown reasons. When this happens, you may receive a diagnosis of unexplained infertility.

Many of the conditions that cause the corpus luteum defect  also cause infertility or miscarriage.

Symptoms of corpus luteum defect:

Symptoms of a corpus luteum defect  can include:

  1. Early pregnancy loss or recurrent miscarriage;
  2. Frequent or short periods;
  3. Stains;
  4. Infertility.

How long does the corpus luteum last?

After a woman ovulates, the corpus luteum only lasts for about 12-14 days unless she starts receiving HCG (human chorionic gonadotropin) from a developing embryo. If the egg is not fertilized, the corpus luteum  dies and progesterone production stops. When progesterone levels decrease, the lining of the uterus stops getting thicker and is consequently shed during menstruation.

If the egg is fertilized, the corpus luteum will begin to receive HCG from the embryo. HCG tells the corpus luteum to keep producing progesterone. The corpus luteum  lasts for about ten weeks after ovulation. After ten weeks, the placenta takes over progesterone production until the end of pregnancy.


There is no standard test used to diagnose the corpus luteum defect . Your doctor will likely recommend hormonal blood tests to measure your progesterone level. They may also recommend vaginal ultrasounds to visualize the thickness of your uterine lining during the luteal phase.

Another possible diagnostic test is an endometrial biopsy. This biopsy is done two days before you expect your period. If your periods are irregular, your doctor will schedule the test sometime after the 21st day of your cycle. For this test, your doctor will remove a small part of your endometrial lining to look at under a microscope.


If you are not ovulating regularly or at all, your doctor may try stimulating ovulation with medications, such as clomiphene (Clomid, Serophene) or injectable gonadotropins, such as human chorionic gonadotropin (hCG). These drugs can be used alone or in conjunction with procedures such as intrauterine insemination or in vitro fertilization (IVF). Some of these medications increase your chances of having twins or triplets.

Your doctor may prescribe a progesterone supplement for you to take after ovulation occurs. Progesterone supplements are available as oral medications, vaginal gels, or injectable solutions. You and your doctor can discuss the pros and cons of each to determine which one is best for you.

If you are having early or recurrent miscarriages due to a corpus luteum defect , your doctor will likely prescribe progesterone without the need for additional medication to increase ovulation.

Design tips:

There are things you can do to help preserve or maintain fertility, which can help you conceive more easily:

Keep your body mass index in the normal range. Being overweight or underweight can have a negative impact on hormonal health.
Know your family history. Some infertility diagnoses seem to run in families. These include polycystic ovary syndrome (on either the father’s or mother’s side), primary ovarian failure (formerly known as premature ovarian failure), and endometriosis. Celiac disease can also affect fertility.
Maintain a healthy lifestyle, which includes not smoking cigarettes, eating a balanced diet, reducing your carbohydrate intake, and exercising regularly.

Reduce your stress level with meditation, yoga or deep breathing exercises.
Consider acupuncture. Studies have found a positive correlation between conception and acupuncture. There are also better conception rates among women who received acupuncture to decrease stress and increase blood flow to the uterus.
Avoid toxins, known as endocrine disruptors, in the environment. These include coal by-products, mercury, phthalates and bisphenol A (BPA).
Track your ovulation with a reputable at-home testing device. Do not use ovulation apps or a basal body temperature thermometer.

Useful links: 

Talk to your doctor if you’ve been trying to conceive for more than a year if you’re younger than 35 or older than six months if you’re 35 or older. Your doctor can help you come up with a plan to improve your chances of conception.

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