The Luteal Phase: Why You Should Know About It

The luteal phase often gets a lot of attention relative to the follicular phase because of its relationship with pregnancy, either in preventing one or becoming pregnant.

It is also essential for the initial maintenance of the early pregnancy.

An understanding of this phase of the cycle is therefore necessary for every woman.

This article presents the necessary basic medical information, simply presented for every woman to understand including its importance, associated uterine and ovarian changes, luteal phase length and common abnormalities seen in some women.

What Is The Luteal Phase?

It is the last phase of the ovulation cycle. It is the period that follows the release of the egg (ovulation) to the day before menstrual flow. Because this phase includes the days that follow ovulation, it is commonly referred to as "Days Post Ovulation(DPO)".

The major contribution of this phase is pregnancy related. It is geared towards making "all ready" to properly establish an early pregnancy. Any abnormality in it thus makes it difficult to retain an early pregnancy.

It is associated with changes in hormonal levels, ovarian follicles and uterine endometrium.

Changes in Ovarian Follicles

At ovulation, the mature follicle ruptures and releases the egg. The remnants of this follicle transforms into another structure called the corpus luteum(yellow body, literally). The cells called granulosa cells which surround the ovum as it matures during the follicular phase become filled with secretions and fat after ovulation, and are called lutein cells or yellow cells.

The main particularity of the lutein cells is that they are capable of secreting the hormone called progesterone and also some estrogen.

The outcome of the corpus luteum depends on the outcome of the egg-whether it is fertilized to produce a pregnancy or not.

• If pregnancy does not occur, the corpus luteum will not receive the support it requires from a developing pregnancy. It then atrophies or shrinks within the ovary. It simply dies. The length of the Days Post Ovulation is dependent on the lifespan of the corpus luteum.
• If pregnancy occurs, the corpus luteum will be sustained by a hormone produced from the developing pregnancy called human chorionic gonadotrophin(hCG,used for pregnancy tests). It will then become bigger, producing more hormones until the placenta within the uterus becomes fully developed and takes over from it.

Hormonal Events

As with the rest of the ovulation cycle, the observed changes are always due to hormonal changes. The main hormone that controls the activities of the luteal phase is progesterone.

The main effects of progesterone during this phase are

1. Mild but detectable elevation of the basal body temperature( About 0.25 to 0.5 degrees Celsius or 0.5 to 1 degree Fahrenheit). Many think of this process as making the body become a sort of biologic incubator to provide a conducive environment for any fertilized egg to develop.
2. Preparation of the uterus for the insertion of any fertilized egg(called blastocyst).The uterus becomes thickened with secretions and blood vessels,making reservations should a blastocyt arrive.
3. Suppression of the production of hormones from the pituitary gland that promote further follicle growth and release of another egg. Why this effect? There should be no release of another egg if a pregnancy is on its way to establishment!

Pregnancy-Related Function

The lifespan of the egg after its release is 24 hours or less.

If fertilized, usually in the fallopian tube, it moves through the tubes into the uterus. Within the uterine cavity, the blastocyst digs into the endometrium and becomes embedded within it. This is called implantation.

It usually takes about 5 to 6 days following ovulation for the fertilized egg to arrive the uterine cavity.

Within the endometrium, the blastocyst requires the support of the endometrium to stay alive. The endometrium itself requires progesterone from the corpus luteum to maintain the conducive environment. If the corpus luteum does not stay until the blastocyst is fully implanted and starts producing hCG to support it, the pregnancy will not be supported. This is the central abnormality of the disease called luteal phase defect.

Importance of this Phase

Why is this phase apparently so important for most women? First, I have realized that the majority of women who have asked for more information on this phase are those who are seeking to achieve a pregnancy.

The medical importance and reason for the popularity of this phase amongst women are due to the factors below.

1. The length of the DPO is critical for the survival of an early pregnancy. An abnormally short luteal phase makes the occurrence of pregnancy very unlikely.
2. The DPO length can also permits a woman to determine the time of ovulation and hence used in fertility planning. By subtracting the length of the luteal phase from the length of the entire cycle, the result is the likely day within the cycle that ovulation will occur. Remember this is just an approximation.
3. Some women have also used this to determine the likelihood of a possible pregnancy. If the time of ovulation is known and menses fail to occur after the length of the luteal phase, an early pregnancy can be suspected even after just one or two days.
4. Finally, the length of this phase has been used by some women to determine the onset of the next menses. Menses can be well predicted if the length of this phase is known as well as the time of ovulation. Menses will occur after the known length of this phase.

Luteal Phase Length

The length of this phase is critical for the survival of an early pregnancy. It is the number of days from the moment after ovulation to the day before menses, normally ranging from 12 to 16 days. A shorter length than 12 days is called Luteal Phase Defect(LPD) and is often associated with miscarriages or infertility. It can usually be measured by using ovulation signs or hormonal kits.

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