The cyclic flow of hormones

Let's have a look at the basics and check out what is happening during the menstrual cycle. 

Between your menarche (that's your first period ever) and your menopause (that's your last period in life), your hormones are flowing periodically - that's the menstrual cycle.


Where are the starting and endpoints?

The four hormones as main players.

And my fertile days? 


Where are the starting and endpoints? 

By definition, the first day of the period sets the start of the menstrual cycle and that's the date you should record in your agenda to have an idea about your cycle length (and to have a date to tell your OB/Gyn in the next consultation, she/he will definitely ask for it).

Your period is of normal duration if it lasts three to six days
and a normal duration of the menstrual cycle if it lasts 26 and 35 days.
A regular menstrual cycle is the best indicator of a balanced hormonal state.

But don't worry if your cycle is irregular - there are a lot of situations in which your cycle could vary, for example, the first years after menarche and the years before menopause - we call that pre-menopause.

If your cycle is frequently irregular, or if you cannot identify a pattern, please ask your OB/Gyn for advice - and don't forget to bring your menstrual calendar.

There are four hormones 
as the main player of this flow:

Two of them have a modulating effect: FSH and LH

The FSH (follicular-stimulating hormone) controls mainly the first part of the cycle - the follicular phase. 
In this approximately 14 days, the follicle (that is a bubble containing the egg cell) is growing in the ovary, until it relives the ovum - that is what we call ovulation (= middle of the cycle). 

Just before ovulation, the level of luteinizing hormone (LH) rises abruptly - this LH-peak marks the onset of the second phase: the luteal phase, which ends with the next period.

These two you might know: Estrogen and Progesterone

Estrogen levels increase during the follicular phase, as it is produced by the growing follicle. After ovulation, when the follicle turns into a luteal body, it produces Progesterone during approximately 12 to 14 days, until the next period starts. These two hormones affect a lot of tissues and functions in our bodies, not only in the reproductive system. 

A lot of women can actually feel the impact of the rising and falling of hormone levels - for example as sore boobs, different sexual desire, mood swings or headaches. 
In various of the blog posts, we will discuss the diverse effects of these hormones.

Figure 1: hormones and menses
Corrine K Welt, MD: Physiology of the normal menstrual cycle. In: UpToDate, Post TW (Ed), UpToDate, Waltham, MA. (Accessed on April 16, 2020.)

And my fertile days?

Hormonal effects on the endometrium

During the follicular phase, the inner lining of the uterus - we call it endometrium - thickens under the influence of estrogen. 
Then, after ovulation, progesterone modifies the endometrium to get prepared for the potential conception of the fertilized egg. 

The day of ovulation and the one before are the most fertile,

but the fertile period ranges from 5 days before to 2 days after ovulation. Knowing these days is important for you - if you want to become pregnant or if you want to avoid conception! However, it is not advisable to use only the calendar rhythm method as your birth control method, especially if you have unregular periods. 
If you would like to use a natural birth control method, I would recommend the Natural Cycles Application. With this tool, you can track your period, your basal temperature and other symptoms and in so doing, determine your fertile period.


A normal menstrual cycle lasts 26 to 35 days and starts with the menstruation.

LH and FSH are regulating hormones.

The follicular phase is dominated by Estrogen.

In the luteal phase, Progesterone becomes the main player, but Estrogen plays still a role.

Estrogen and Progesterone affect the condition of the endometrium.

The fertile period ranges from 5 days before to 2 days after ovulation.

Figure 2: menstrual cycle
Corrine K Welt, MD: Physiology of the normal menstrual cycle. In: UpToDate, Post TW (Ed), UpToDate, Waltham, MA. (Accessed on April 16, 2020.)

This post was written and last edited by Carmen, April 20th 2020