Understanding the menstrual cycle

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Understanding the Menstrual Cycle


Thank you to Allyn, for so kindly writing this amazing piece for us. Allyn works with us as one of our fit and fab collective coaches.

I chose this topic first because so many of my patients don’t understand their menstrual cycle in regards to getting pregnant or even avoiding pregnancy.

Let’s start at the beginning. Cycle day 1 is considered the first day of full flow bleeding. Many women have spotting before, but in the medical world, we don’t count that as the actual period.

The days following the start of the period are called the “follicular phase” because it is when the follicle grows (the egg is inside the follicle). As the follicle grows, it puts out estrogen. 
This estrogen has 2 functions in the follicular phase. 
First, it will cause the lining of the uterus (called the endometrium) to get thicker in preparation for a potential pregnancy.
Second, after the follicle gets to maturity, the level of estrogen is about 150-200 and after it remains that high for so long, it causes an LH surge. The LH surge indicates an ovulation in the next 24 hours.

Now a quick note on the LH surge

an LH predictor kit can pick up any level over about 10 but it can go as high as 90 or above so you do need to test every day during your fertile days or you won’t know if you picked up the surge on the way up or way down. But if you don’t like LH kits I have a better suggestion later in this post!

Once you have ovulation, then the progesterone rises (it stays below 1 prior to ovulation)

 This starts the luteal phase. The progesterone will continue to rise for a week after ovulation usually hitting at least a 10 before dropping again (if there is no pregnancy). If the body does pick up a pregnancy then the progesterone will continue to rise and the follicle that ovulated will put out the progesterone to support the pregnancy until 6-8 week of gestation when the placenta takes over.

Progesterone is the hormone that supports the pregnancy. It is a smooth muscle relaxer (we want the uterus to stay relaxed and let that pregnancy implant!) The only bad part is that it is not selective to the uterus- so you can thank progesterone for the pregnancy symptoms of constipation (the bowels relax and slow down movement) and heartburn/reflux due to the upper GI tract having some decreased muscle contraction.

If there is no pregnancy then a week after ovulation, the estrogen and the progesterone will drop and this drop will induce a bleed approximately 2 weeks after the ovulation.

So- there should always be around a 14 day time period between ovulation and a period. This is where “cycle length” gets confusing for many people. Ladies with a 28-day cycle will have a 14 day follicular phase and a 14 day luteal phase. This is where we get the “normal cycle length” from. However, if you have longer cycles then it is just the follicular phase that varies. For example- if you have a 28 day cycle then you ovulate on cycle day 14 (followed by a 14 day luteal phase). If you have a 32 day cycle then you ovulate on cycle day 18 (followed by a 14 day luteal phase). You may also have a shorter cycle. That means if you have a 26 day cycle then you ovulate on cycle day 12 (followed by a 14 day luteal phase).

To recap- your luteal phase (from ovulation to period) should always be around 14 days but the time it takes to grow the egg and ovulate can vary between women.

So, if you want to get pregnant and don’t want to take LH kits

The best thing to do is to have intercourse on cycle days 10-20 every other day and that covers you if you have a cycle between 24-34 days. If you have a cycle longer than that then you just subtract 14 days from your first day of your period and you know what cycle day you ovulate. For example, if you have a 60 day cycle then you ovulate around day 46.

A second thing to consider when trying to conceive is the timing of intercourse. The sperm can live in the body for 3-5 days but once the egg ovulates, it is usually available for fertilization for only 12-24 hours. This means it is more important to have intercourse in the 1-2 days prior to ovulation so you have sperm available for the egg.

On the flip side, if you are trying to count cycle days and NOT get pregnant then you would need to use protection as soon as 5 days prior to ovulation and 2 days after. I would only use this method if you have VERY regular cycles.

Ok, that is the menstrual cycle in a nutshell. 
Leave any questions you have in the comments section.
Allyn Ann Simpson
MSN, WHNP-BC

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