LUNA explains : The different stages of the menstrual cycle

The first stage of the menstrual cycle is the period. The first day of menstruation represents the first day of the menstrual cycle. Bleeding is usually heaviest on the second day. The endometrium is very thick. It has thickened during the last cycle, to allow the development of an embryo. It’s then eliminated, which creates the bleeding. The follicles remain the same size in the ovaries at this stage.

This is the end of the endometrium elimination and therefore the period’s end. There may be some minor bleeding left. The follicles develop in the ovaries and are of different sizes. There are 4–5 follicles, which are created by FSH. Due to the low estrogen level, the hypothalamus will be stimulated, which will secrete GnRH (Gonadotropin-Releasing Hormone) then FSH (Follicle Stimulating Hormone) and LH (Luteinizing Hormone produced by the pituitary gland).

The follicles keep developing in the ovaries, secreting estrogen. They will allow the uterine lining (endometrium) to thicken and begin to grow.

The endometrium continues to thicken. In the ovaries, one follicle develops more than the others: this is the dominant follicle. At this time, a positive feedback from the pituitary gland will release a peak of LH which will allow ovulation by the dominant follicle.

This is ovulation. The endometrium has reached its maximum thickness. In the ovary, the follicles diminish, except for the dominant follicle which will release the oocyte into the fallopian tube, then transform into a progesterone-creating corpus luteum during the second part of the menstrual cycle.

This is the second phase of the menstrual cycle. The endometrium is no longer developing thanks to the secretion of progesterone from the corpus luteum. The oocyte has moved along the fallopian tubes to the uterus.

The uterine lining remains very thick, and the ovary contains only the corpus luteum. If the egg is fertilized, the corpus luteum of the dominant follicle will prevent the menstrual phenomenon from occurring. If not, it will be destroyed, and a new menstrual cycle will begin with the menstrual period. The oocyte has disappeared from the uterus.

Scientifically validated by Dr Jean-Philippe Estrade,

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