The menstrual cycle, often referred to as your period, is a natural, physiological phenomenon beginning in early adolescence and ending at the menopause. This monthly cycle requires the perfect coordination of various organs (brain, ovary, uterus) and the means of communication your body has available (neurons and vessels). Each woman therefore has her own menstrual cycle depending on her age and contraceptive habits.

Why is the menstrual cycle necessary?

The purpose of the menstrual cycle is to allow the ovulation of an oocyte (egg) in preparation for a pregnancy, which will develop in a uterine lining (endometrium) that is regenerated every month. In the absence of pregnancy, this endometrium will be discharged through menstruation. This is a cyclical process that takes place over 28 days.

How the menstrual cycle works?

This physiological phenomenon affects women of childbearing age, from puberty to the menopause.

Changes in the uterine lining, along with ovarian function that leads to ovulation, depend on a hormonal system orchestrated by your brain.
The sequence of these interactions is called the hormonal cycle. It begins in the brain inside your hypothalamus-pituitary complex, located at the base of the skull:

These two hormones are in direct contact with your ovaries via the bloodstream:

  • FSH will stimulate the ovaries and cause the follicles carrying the oocytes to grow (folliculogenesis)
  • LH will increase in the middle of the cycle, creating an LH peak and triggering ovulation.

Once stimulated, your ovaries will cause the secretion of oestrogen and progesterone which will alternately allow the growth of your uterine lining and its preservation after ovulation, to accommodate a possible pregnancy. The secretion of oestrogen also controls the LH and FSH secretion to harmonise your hormonal cycle.

If a pregnancy develops, your uterine lining will remain intact and your period will be absent. On the other hand, the absence of a pregnancy will cause progesterone to collapse and your period (a mixture of blood and fragments of uterine lining) to appear.[/

Different stages of your menstrual cycle

Your menstrual cycle consists of three stages: the follicular phase (growth of the follicles containing the oocytes), ovulation and the luteal phase (preservation of the uterine lining).

LUNA Memo:

Day 1 to 14: the follicular phase

The follicular phase is the period between the 1st and 14th day of your cycle. This phase therefore begins on the first day of your period. During this phase, FSH enables the ovary to grow 4 to 5 follicles, so that it can select one: the dominant follicle. These follicles will secrete oestrogen which will allow the lining of the uterus to develop, until it reaches the thickness necessary for the development of a possible embryo. The duration of this phase can vary.

Day 14: the ovulation phase

The ovulation phase occurs on day 14. This phase allows the dominant follicle to release the oocyte into the fallopian tube. The dominant follicle will transform into a corpus luteum, which will secrete progesterone during the last part of the menstrual cycle.

Day 14 to 28: the luteal phase

The luteal phase is the period between days 14 and 28 of your cycle. The progesterone secreted by the corpus luteum has an adverse effect on the FSH and LH, acting as a brake. During this phase, the endometrium is kept thick by the secretion of progesterone by the corpus luteum. In the event of fertilisation, the corpus luteum is sustained and will prevent your period from occurring. In the absence of pregnancy, the corpus luteum will be destroyed and the absence of progesterone will cause menstruation. The hormonal cycle will then start again


Only the luteal phase is constant and lasts 14 days. In contrast, your follicular phase can vary, resulting in a longer or shorter menstrual cycle. The day of ovulation is therefore calculated according to the length of the usual cycle.

LUNA helps you :

The LUNA CALENDAR feature will allow you, based on your menstrual cycle data, to:

– predict your period

– determine the day of ovulation to predict or prevent pregnancy.

The menstrual period

Menstruation is a loss of the uterine lining through vaginal bleeding over a period of 3 to 8 days.

It’s a complex and unique phenomenon in the body, involving many inflammatory mechanisms.

To renew the endometrium quickly, the uterus uses:

  • a reduction in blood flow,
  • significant swelling,
  • the influx of white blood cells, releasing proteins from the inflammation.

These three actions combine to produce the prolonged inflammation necessary to destroy your lining, then reverse the process to generate new lining growth.

These rapid changes create an instability that can affect the way you view your period, especially in terms of pain and bleeding

For more information : Menstrual cycle and age

The hormonal cycle will change somewhat as you age, which explains the development of different menstrual patterns throughout your life.

At puberty, the immaturity of your hormonal cycle and the “surprise event” of your period can lead to irregular, heavy and painful cycles. This is also the case before the menopause: the hormonal cycle is disturbed and responsible for anomalies such as pain and heavy bleeding.

Your periods therefore change throughout your life and can also change according to your cycle and hormonal state.

read also : Hormonal Cycle, Ovarian Reserve And Fertilityrm

Co-authored and scientifically validated by Dr Jean-Philippe Estrade,

Gynecological surgeon and expert in endometriosis at the Clairval Private Hospital and the Bouchard Clinic, in Marseille.