Four Phases of the Menstrual Cycle

There are four main phases to the menstrual cycle that are governed by your hormones. They are the follicular phase, the ovulatory phase, the luteal phase, and the menstrual phase. Each phase has a specific function and result.

The Follicular Phase

The follicular phase occurs early in your cycle. During this phase the level of follicle stimulating hormone (FSH) is increasing, causing your ovaries to mature the eggs. About five to seven days into this phase a dominant follicle will appear, which has gotten more nourishment from your body than the other follicles.

Your estrogen levels are on the rise. Your luteinizing hormone (LH) is low but rising, and your progesterone levels are low as well. This phase lasts about 10 to 11 days for the average 28-day cycle.

The Ovulatory Phase

The ovulatory phase occurs in the middle of your cycle. Your estrogen levels rise rapidly from about day 10 until day 15, at which point it decreases again. During this phase you will have a smaller surge of the FSH to begin ovulation, with a large rapid surge of LH.

Because it is no longer needed to house the oocyte, the dominant follicle begins to collapse during this phase, causing your body to produce more progesterone to help build and maintain the lining of your uterus should the egg fertilize.

The Secretory Phase

It is during this secretory phase that your endometrium, or uterine lining, builds. This lining will be the home of your new baby until birth, should pregnancy occur. If you do not get pregnant during this cycle, the lining is sloughed off during your period as you go through progesterone withdrawal. This phase usually lasts about 13 days.

During the secretory phase, your ovaries are also going through the luteal phase. Your luteal phase finds your LH levels and FSH levels returning to normal. Your estrogen levels are not as high as they were at their peak, but are still above their baseline levels. However, your progesterone levels surge until the end of this phase.

Do all women experience PMS?

Premenstrual Syndrome (PMS) occurs in about 40 percent of women. During PMS, you experience physical and emotional reactions to the hormonal process going on in your body. You may experience bloating, irritability, or food cravings, among other symptoms, according to the American Congress of Obstetricians and Gynecologists (ACOG).

The Menstrual Phase

The menstrual phase is just what it sounds like. If pregnancy has not occurred, the spot on your ovary where the last egg was released, called the corpus luteum, begins to die and your menstrual cycle begins. If a pregnancy has occurred, the corpus luteum will produce hormones until the production of those hormones is taken over by the placenta, around 12 to 14 weeks gestation.

As your corpus luteum collapses, your progesterone levels fall and your body begins to cleanse itself of the uterine lining. Typically, menstrual bleeding will last four days, though it can last anywhere from two to eight days. The average length of your cycle will probably vary. The average cycle lasts 28 days, but it is perfectly normal to have a cycle ranging anywhere from 21 to 35 days in length.

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