Fertility 101: What Your Monthly Cycle Says About Your Fertility

fertile menstrual cycle

It wasn’t until I started having issues with my menstrual cycle that I really learned anything about it. Unfortunately, that seems to be the case for so many women these days: we only start looking into what a healthy, fertile cycle is when we don’t have one!

In my case, I decided I didn’t want to rely on the birth control pill to control my acne any longer. But, every time I went off of it, my acne would return with a vengeance, and in a new twist since beginning hormonal birth control, my period would be irregular, and then disappear completely within three months. I figured that there had to be ways to support my body coming off of the pill. And that’s why I got up close and personal with the menstrual cycle and everything to do with it.

Our cycles can tell us so much about our health and fertility every single month. We just need to know what to look for.

What happens in a fertile cycle?
There are two predominant sex hormones in the female reproductive cycle: estrogen and progesterone. These two hormones go through a delicate dance each month, inducing ovulation, growth of the uterine lining, followed by shedding of the lining or conception.

A new cycle starts with the first day of bleeding. This initiates what is known as the ‘follicular phase’ of the cycle. The first few days of the period, levels of estrogen and progesterone are both very low. During this time, the hypothalamus scans the body for levels of estrogen and progesterone and registers that both are very low. It then communicates to the pituitary gland that it needs to start producing follicle-stimulating hormone (FSH).

FSH travels to receptors on the ovaries, which communicate to the ovaries that it is time to start producing estrogen. It also causes one of the follicles on the ovary to begin to grow. This follicle contains an egg.

Spoiler alert: we don’t all have twenty-eight day cycles.

Growing estrogen levels also stimulate the growth of the uterine lining and increased production of cervical fluid. In the days leading up to ovulation, more and more cervical fluid is produced, and it changes in quality so that it can both feed sperm and help them to swim up the fallopian tubes to where the egg will be (should sperm be introduced to the reproductive system during this time).

When estrogen levels reach a certain threshold, the hypothalamus registers this hormonal change and communicates to the pituitary gland that it is time to release luteinizing hormone (LH). This LH surge triggers ovulation, although it usually occurs about two days beforehand. This is the hormone detected by ovulation prediction kits.

Once LH triggers ovulation, the egg is released from the now mature follicle, and is caught by fringe-like tissue called fimbria on the fallopian tube and guided into it. The ruptured follicle that the egg departed from, becomes what is known as the corpus luteum. It remains on the ovary and begins to produce progesterone, which becomes the dominant hormone during the second half of the cycle as estrogen levels drop. This phase is known as the luteal phase.

Progesterone nourishes the uterine lining, which developed because of the preceding estrogen levels, and keeps it intact for as long as the corpus luteum survives. If the egg is fertilized, it will typically be fertilized in the fallopian tube, and then travel toward the uterus, where it will implant in the uterine wall. Implantation leads to the release of yet another hormone, human chorionic gonadotropin (HCG), which keeps the corpus luteum intact and producing progesterone until the placenta develops and is able to take over.  This is the hormone detected by pregnancy tests.

If fertilization does not occur, the corpus luteum dies within about two weeks. This causes progesterone levels to drop and the uterine lining to shed, resulting in a period and a new cycle!

Indicators of Fertility:
I realize that was a lot of information, so let’s focus on the important parts for fertility. There are three key ingredients to a fertile cycle.

Cervical fluid
Because the egg only lives for 24-48 hours once released, there is a fairly small window for conception. Adequate levels of fertile cervical fluid help to nourish sperm and enable them to swim up to the egg. Cervical fluid that is present at non-fertile times of the cycle actually has an unfavorable pH for sperm and reduces motility. Fertile cervical fluid contains channels that the sperm can swim through and helps to create a more favorable environment for sperm. Fertile cervical fluid can also extend your fertile window by enabling sperm to live in your reproductive tract longer.

Obviously, if no egg is released, then there can be no fertilization!

Sufficient luteal phase
The uterine lining has to stay intact long enough to allow for implantation. The time between ovulation and the first bleeding day has to be at least nine to ten days long to enable implantation. If the luteal phase is shorter than this, the egg may be fertilized but will leave the body with the period before implantation.

Monitoring your cycle
A great way to keep tabs on your fertility is to track your cycle and take note of changes in cervical fluid, ovulation and the length of the luteal phase. This can help to reveal what your unique cycle looks like. (spoiler alert: we don’t all have twenty-eight day cycles). It can also help you discern whether or not you are ovulating each month, and if you have a sufficient luteal phase. Changes in your unique pattern can also indicate health issues or changes in your fertility.

The information provided above is for informational purposes only and should not be construed as medical advice or a substitute for medical care.

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