The menstrual cycle is the monthly hormonal cycle a female’s body goes through in preparation for a possible pregnancy.

Having regular menstrual cycles means that essential parts of your body are working fine. The menstrual cycle supplies important body chemicals (known as hormones) to keep you healthy, and prepares your body for pregnancy each month.

There are four parameters to define normal menstruation. They are:

Frequency. Normal frequency is the onset of menstrual bleeding every 24 to 38 days.

Regularity. When assessing regularity, cycle length is defined as the number of days from the start (day 1) of one period until the start (day 1) of the next period.

Duration. The normal number of bleeding days in a single menstrual period is less than 8 days.

Volume. Normal volume is subjective and defined as menstrual blood loss volume that does not interfere with a patient’s physical, social, emotional, and/or material quality of life.

The menstrual cycle is divided into two phases, and they are the follicular and luteal phase.

Follicular Phase

The start of this phase is marked by the start of the menstruation, and ends on the day before the luteinizing hormone (LH) surge.

Days 1-5 (on average)

If there is no pregnancy, the thickened uterine lining is shed. It exits the body through the vagina as menstrual blood.

Day 14

Every month, one of the ovaries releases an egg cell. This egg cell travels through the fallopian tube, towards the uterus.

This stage is also known as ovulation, or fertile days, when chances of getting pregnant is at its peak.

Luteal Phase

This phase begins on the day of the LH surge and ends at the onset of the next menstrual bleeding.

Days 15-28

The uterine lining becomes thicker to prepare for a fertilized egg cell. If there is no pregnancy and the egg cell remains unfertilized, it will just dissolve in the reproductive tract.

Sources:

https://www.nhs.uk/conditions/periods/fertility-in-the-menstrual-cycle/

https://www.healthline.com/health/womens-health/stages-of-menstrual-cycle#follicular

https://www.sciencedirect.com/topics/medicine-and-dentistry/menstrual-cycle

https://fphandbook.org/menstrual-cycle