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Proliferative Phase
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Proliferative Phase

September 28, 2023


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If The Beatles wrote a song about the menstrual cycle, it might go something like this: “To every cycle (turn, turn, turn) there is a phase (turn, turn, turn), and a time for all your body’s hormone changes.”

Unfortunately, the complicated changes that happen to our endometrium throughout the month aren’t likely to be celebrated in song form anytime soon. But we still think it’s worth learning about.

Take a minute to think about the menstrual cycle and the different phases it contains. You’re probably pretty well versed on what happens in your body during menses and ovulation, but how much do you know about the proliferative phase of your menstrual cycle? If you responded with, “the what phase?” that’s totally OK. The proliferative phase is often overlooked in casual menstrual cycle discussions.

We don’t think the proliferative phase gets enough attention, so let’s learn about it. The truth is, this phase of your menstrual cycle is one of the most important, as it helps prepare your body for ovulation. If things don’t go right during this phase, it could affect your ability to ovulate and conceive.

If you have any interest in becoming a parent, you should get nice and cozy with your proliferative phase and how it works. Let’s dive right in.

What Is the Proliferative Phase?

We thought you’d never ask! The proliferative phase of your menstrual cycle occurs after your menstrual phase and helps prepare your endometrium (which is just a fancy word for the lining of your uterus) for a potential pregnancy. The goal of this phase is to achieve optimum endometrial receptivity, which is the process that allows the embryo to attach to the endometrial lining and develop.

This phase of your menstrual cycle is approximately 14 days in length (from the end of your period until the beginning of ovulation), based on an average menstrual cycle duration of 28 days. During this phase, your estradiol (a form of estrogen) levels increase rapidly. As estrogen increases, it triggers changes to the endometrium. The endometrium becomes thicker and continues thickening until ovulation. The uterine lining must change in this way to create the right implantation environment for a fertilized egg. Cervical fluid also increases and becomes more slippery during this phase.

The proliferative phase is commonly known as the follicular phase since it’s also the phase when the ovarian follicles mature. At the beginning of the follicular phase, many follicles are developing and vying for dominance. They’re surrounded by granulosa cells that help protect them. An increase in FSH stimulates the production of granulosa cells. Granulosa cells produce hormones, including estrogen, progesterone, and anti-Mullerian hormone.

Eventually, most of the follicles in the ovary die off and one emerges as the Graafian follicle. This is the follicle that will release the mature egg. It will later become the corpus luteum during the luteal phase, which comes after the follicular phase. The corpus luteum is a progesterone-secreting endocrine gland. If an egg is not fertilized, the corpus luteum will regress.

How Can the Proliferative Phase Be Subdivided?

The proliferative or follicular phase of the ovarian cycle can be subdivided into early, mid, and late phases. There are a lot of changes during these phases, including changes to endometrial thickness and uterine glands.

During the early phase (which occurs immediately after menses), the endometrium begins to regenerate and forms a thin endometrial tissue layer. The endometrium begins to heal and strengthen itself after the effects of menstruation. Granulation tissue is involved in this process, just as it’s involved in wound healing in other parts of the body. The uterine glands during this early phase are straight, short, and narrow. The endometrial stroma contains cells that are closely bunched and spindle-shaped.

During the mid-phase, occurring during the follicular phase (which spans from approximately day 8 to day 10 of the menstrual cycle), columnar epithelial cells within the uterine glands become more curved and elongated.

In the late phase, also occurring during the follicular phase (around day 11 to around day 14), the endometrial glands become more closely packed and coiled. They also begin to undergo nuclear pseudostratification and active mitosis (cell division).

Throughout the various phases, cervical fluid changes. It becomes more thin, watery, and slippery. The changes also make the vagina less acidic, so it’s a more hospitable environment for sperm.

Can You Feel the Proliferative Phase?

If you’re interested in tracking your menstrual cycle and the times when you’re most fertile, you may be wondering if you can feel the proliferative phase. Some women can feel some changes during this phase, such as increased energy, backaches, or increased confidence. You can also pay attention to your cervical mucus to get an idea of where you’re at in your menstrual cycle.

At the beginning of the follicular phase, cervical mucus tends to become slightly sticky and creamy. Around the time of ovulation, it becomes more slippery, stretchy, and clear.

What Happens After the Follicular Phase?

After the follicular phase, your body will enter the secretory phase. During the secretory phase, you’ll experience an increase in progesterone levels that prepare the uterine wall for the potential attachment of a fertilized egg. The process that increases endometrial thickness comes to a halt during this time.

If you don’t become pregnant during the follicular phase, your body will break down your uterine lining during the secretory phase. Endometrial cells secrete prostaglandins, which stimulate contractions in the uterine muscle. In other words, those little buggers cause your uterus to cramp up. This cramping in your uterus helps trigger menstruation.

In addition to cramping, the corpus luteum also stops producing progesterone and estrogen. As these hormones drop, the blood vessels constrict, and endometrial tissue begins to break down. As menstruation begins, your body’s remarkable menstrual cycle starts all over again.

Is Proliferative Phase Endometrium Normal?

Proliferative endometrium is a term that refers to healthy reproductive cell activity. When your body prepares a layer of endometrial cells for attachment of a fertilized egg, that layer is called proliferative endometrium.

If this normal process ever leads to the unusual growth of endometrial cells, it’s referred to as disordered proliferative endometrium. Usually, this term is used to describe abnormal endometrial thickness. In some cases, though, it can be a sign of a serious problem that should be addressed with help from your OBGYN.

If the endometrium becomes too thick during the follicular phase, it’s referred to as endometrial hyperplasia. In some cases, this may not be a cause for concern. But you should know that it can potentially lead to cancer of the uterus, so you should monitor it carefully.

Which Phase of the Uterine Cycle Is Driven by High Levels of Estrogen?

High estrogen levels drive the follicular phase of the uterine cycle. The anterior pituitary gland releases additional hormones during the follicular phase, including follicle stimulating hormone (FSH) and luteinizing hormone (LH).

Discover the Hormone-Balancing Secret

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