Menstrual Cycle, Hormones and Fertility

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Mario Fernando

By Mario Fernando

When you menstruate, you may notice vaginal bleeding, abdominal pain, headaches and other physical symptoms. However, there is a lot more happening behind the scenes. The menstrual cycle is a way of your body preparing itself for ovulation and fertilization, but there are five key hormones that are responsible for this.



Pituitary gland and its position

How do these hormones control the menstrual cycle?

These hormones work together in a hierarchical structure to establish four phases of the menstrual cycle.

  1. Follicular Phase
    This phase occurs in the first 14 days of a regular 28-day cycle. Due to a drop in the levels of all five hormones, the uterus wall layers begin to deteriorate, along with some of the underlying blood vessels. Hence, menses (menstruation) makes up the beginning of this phase, generally for around 3-5 days. Despite the low levels of hormones, FSH and LH levels are still high enough to stimulate some follicular growth during menstruation.

    What is a follicle? Think of a follicle as a nurturing capsule for an egg. You are born with a certain number of follicles, and each cycle, a few of these are stimulated to grow. One of these grows large enough to ovulate, whilst the others degenerate. The follicles respond to FSH and LH, and produce estrogen and progesterone.

    The part of the follicular phase after menses is when some hormones begin to flux. Firstly, a gradual estrogen surge occurs from around the 3rd to the 14th day as the dominant follicle responds to the baseline, low levels of FSH and LH. It is important to know that every change in hormone levels has a purpose. In this case, the climbing estrogen levels repair the damage to the uterus lining after menses and causes the endometrium to thicken in preparation for implantation.

    Next, GnRH is secreted in rapidly increasing amounts from the hypothalamus in your brain. It tells the pituitary gland near it to start producing FSH and LH. This causes a sharp LH surge and an FSH spike. These travel in your blood and eventually reach your ovaries where they cause the dominant follicle to release its egg. This surge is a very important part of the cycle as it is what causes ovulation, as well as an increase in your basal body temperature. Your basal body temperature will increase from close to 36 degrees Celsius to close to 37 degrees Celsius after ovulation. This is an easy way of knowing when you ovulated.
  2. Luteal Phase
    After ovulation, the dominant follicle does not degenerate. The remaining capsule of the follicle is called the Corpus Luteum - hence, this phase is known as the Luteal Phase. Although the Corpus Luteum no longer contains an egg, is still has a very important job in your cycle. It produces high levels of progesterone and estrogen which peak during the middle of the Luteal Phase and dwindle back to low levels at the end of it. What effects do these two hormones have? Remember, the main purposes of the menstrual cycle are to incite ovulation and prepare a suitable environment for a potential egg and sperm to grow into an embryo. So during the luteal phase, the uterus lining continues to become thicker, has a better blood supply and also starts to secrete more fluid.

    Progesterone also creates the higher basal body temperature. This stage continues from 14 days to 28 days.

    Eventually, the Corpus Luteum degenerates into the Corpus Albicans - a non-functional remnant of the original dominant follicle. This means the production of estrogen and progesterone stops, and if the egg is not fertilized, all hormones fall back to their original low levels. Now the uterus lining degrades again, as menses marks the resetting of the cycle.

How does the cycle change when I do get pregnant?

When a sperm successfully fertilizes the egg, the embryo implants onto the uterus wall. It then releases human Chorionic Gonadotropin (hCG), which is chemically very similar to LH. This is the chemical that pregnancy tests look for. Circulating hCG extends the life of the Corpus Luteum and prevents it from degenerating. The Corpus Luteum is able to continue releasing estrogen and progesterone which allows the development of the embryo to proceed. Because of this process, menstruation does not occur.

Struggling to understand all these hormone details?

All this information is easily understood by looking at the image below.

Menstrual cycle hormones

Let us know what you think by leaving a comment below.

New Join the Discussion!

  1. Ifeoluwa Sep 03, 2016
    After all this explanation, if you later see blood on the 28th and 29th day of your cycle before your next period, does it mean you are still pregnant?
    1. Christina (OC Team): This depends on your cycle. It could just be an early start to your period, which would mean you are not pregnant. Or if it's light and only lasts 1-2 days, it could be implantation bleeding. Have a look at this quiz https://www.ovulationcalculator.com/implantation-bleeding-or-period-quiz/ - (Sep 03, 2016)
    Reply
  2. Shiketa Oct 01, 2016
    I had a cycle in June. We went to the doctor on July 6th and they said that I was a month pregnant.
    1. Christina (OC Team): Congratulations! - (Oct 01, 2016)
    Reply
  3. Nuella Oct 25, 2016
    I had sex on all the right days acccording to my cycle calender for the first time! Thanks for your help
    Reply
  4. Mia Oct 31, 2016
    I had my cycle a few days ago, but I feel really nauseous and am tired more than usual.
    1. Christina (OC Team): I'm sorry to hear you're not feeling well. - (Nov 01, 2016)
    Reply
  5. Anita Nov 01, 2016
    I had my meanstraution on 29th October, so when am I going to ovulate?
    1. Christina (OC Team): Enter your cycle information into your account here for a prediction. - (Nov 01, 2016)
    Reply
  6. Lincy Nov 16, 2016
    I ovulated on the 14th day after my period, but it ruptured my left ovary. Follicle size is 13 mm. Endometrium thickness on the 16th day. 4mm. Possible pregnancy???
    Reply
  7. Mayra Nov 25, 2016
    I started spotting a week before my period and it was light pink and brownish, but I started bleeding heavier. It was like my period on the day of my menstrual cycle, but I've been feeling pregnancy symptoms. I even started to get veins on my breast. Can I be pregnant ?
    Reply
  8. Mayra Nov 25, 2016
    Is having rising levels of FSH bad ?
    Reply
  9. ZAYNAB Nov 29, 2016
    I have two questions for you
    1. Is it possible to ovulate on CD7??
    2. Which is the best days to BD? Is it every day or every other day?
    Thanks in anticipation of your response.
    1. Christina (OC Team): It's unlikely that you would ovulate on CD7, but it's possible that your fertile window would start this early. Your fertile window occurs in the 6 days leading up to and including ovulation. Most experts recommend BD every other day during your fertile window when TTC. - (Nov 29, 2016)
    Reply
  10. Mia Nov 29, 2016
    Can sex make your period late?
    Reply

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