Period 101 and What Happens in PCOS

Updated: May 3, 2020

Periods are vital in women’s bodies from puberty to menopause. It’s more than the time of bleeding, rather it’s a monthly cycle that your body goes through (not just your reproductive system).

I think it is important to understand how the cycle works for many reasons. Reasons like understanding some symptoms in relation to the cycle such as bloating, anxiety, fertility, etc. The cycle is the body’s preparation for pregnancy, so understanding helps in preparation for pregnancy or preventing it.

Have you ever wondered how our menstrual period happens or how this cycle works?⁠ I did! And I always felt it’s complicated when I first studied it in high school!

Here, Let me explain it simply to you! It’s not complicated after all!

The cycle happens every month. It may differ from month to month. In average the cycle is 21-35 days. It happens as a result of a harmony between hormones and organs. Different symptoms may occur at different phases of the cycle related to the body’s response to hormonal peaks and nutrients in the body.

Menstrual Cycle Hormones 101

Before we start, let’s make sure we get this little backgrounder on the hormones that are involved in this cycle!

There are many hormones that are involved in the monthly cycle, however, the main hormones are:

  1. GnRH: Gonadotropin Releasing Hormone: released from a little structure in the brain called the hypothalamus. It stimulates the pituitary gland to secrete LH hormone.

  2. FSH: Follicular Stimulating Hormone: released from a small gland in the brain called the pituitary gland to stimulate the largest follicle to release the egg.

  3. LH: Luteinizing Hormone:released from a small gland in the brain called the pituitary gland to trigger ovulation.

  4. Estrogen: released after the FSH from the largest follicle (dominant follicle).

  5. Progesterone: released by the empty follicle after the egg release to help thicken the uterus lining for a potential pregnancy.

Hormones work in harmony together, so imagine if there is an imbalance that may happen in PCOS! Read to the end to learn more!

So now we kind of have an idea of the main hormones that are involved in the cycle. Let’s understand this cycle.

  • Everything starts in the brain

The brain has this amazing little structure called: the hypothalamus. Another wonderful structure is the pituitary gland. Both of them work together to release hormones during the cycle.

  • The ovaries

Then the hormones stimulate the ovaries and the follicles to release more hormones.

  • The uterus

The uterus builds a lining inside it to support a possible pregnancy if the egg got fertilized and releases chemicals that cause contractions to release the period if no pregnancy and after the drop of estrogen and progesterone.

The phases By Days

There are two main phases. The number of days below is based on the average cycle. Your cycle may slightly have a different timeline.

  • The follicular Phase

o Day 1: First day of the cycle, which is the first day bleeding (of the period).

o Days 1-5: The days of period bleeding. Period can last anywhere from 3 to 8 days, but 5 days is average.

o Days 6-14: FSH peaks to stimulate the follicles in the ovaries. One dominant follicle matures to release an egg. This phase may last 10-22 days. When the egg is released it releases estrogen. When estrogen is enough, it signals to the brain to increase LH, which causes the ovulation.

o Day 14: Ovulation Day (phase). The uterus starts building a lining again.

  • The Luteal Phase

o Days 14-28 the follicule that released the egg produces progesterone and estrogen. When this follicule breaks down on day 9 or 11 after ovulation. This results in a drop in estrogen and progesterone levels, which causes menstruation.

Many changes in physical and emotional health appear on women throughout the cycle. The following video shows that in a short and fun way:

The Cycle in PCOS⁠

In PCOS the cycle could be longer than average or a period (bleeding) may not occur. PCOS may cause no period or less than 9 periods a year. Periods may look light or heavy with strong painful symptoms around the cycle. This is due to the hormonal imbalances.

These hormonal imbalances start with the GnRH being released rapidly vs regular cyclic rythem. This makes the release of LH (that is why LH:FSH ratio is high in PCOS). The release of high LH increases the androgens, which do not allow for a normal ovulation and menestrual cycle.

High androgens (male hormones) causes issues with ovulation. Lack of estrogen and progesterone do not allow for a completion of menstrual cycle. The egg may not mature, and the uterus lining may mature slowly, which makes the cycle long.

Track your cycle

One good practice is tracking your cycles and your symptoms to have a better understanding of what is going on in your body.

Apps that I found useful and used myself:

In future blogs, I will discuss the symptoms that are associated with the cycle and the nutrition that is important for each.

Stay tuned!


The Society of Obstetricians and Gynecologists of Canada. (2019). Normal Periods: Menstrual Cycle Basics. Retrieved from:

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