What Is the Menstrual Cycle?

Medically Reviewed on 11/4/2022
What Is the Menstrual Cycle
A normal menstrual cycle typically lasts between 24 and 38 days

The menstrual cycle is the monthly cycle of changes that occur in a woman’s body to prepare her for a possible pregnancy. If pregnancy does not occur, there is a discharge of blood and tissue from the inner lining of the womb through the vagina, also known as menstruation, menses, or periods. During menstruation, the inner lining of the uterus is also shed from the vagina.

The menstrual cycle is regulated by various hormones, each controlled by negative and positive feedback mechanisms. Cyclic changes in these hormones are responsible for what happens during a menstrual cycle. The hypothalamus of the brain secretes the gonadotropin-releasing hormone, which in turn stimulates the pituitary gland to secrete follicle-stimulating hormone (FSH) and luteinizing hormone (LH). FSH and LH act upon the ovaries to stimulate the release of the hormones estrogen and progesterone.

What is the normal cycle for menstruation?

A normal menstrual cycle typically lasts between 24 and 38 days. However, any cycle between 21 and 45 days is still considered normal. Monthly periods may vary from woman to woman and can also change over the years.

In a normal cycle of menstruation, there are some events that occur in the ovary and womb (uterus). These events are divided into four phases.

What are the four phases of the menstrual cycle?

1. Menstrual phase

The menstrual phase lasts from day 0 to day 5 of the menstrual cycle. 

During this phase, the uterine lining is shed. Day 1 is considered the day menstrual blood flow begins in the absence of a pregnancy. Bleeding generally lasts 3 to 5 days in most women, although bleeding for as few as 2 days and as many as 7 days is also considered normal. 

2. Follicular (proliferative) phase

The follicular phase starts at the end of the menstrual phase and takes place from days 6 to 14.

Estrogen levels increase during this phase, causing the thickening of the endometrium (inner lining of the uterus). It is called the follicular phase as FSH levels also increase, causing the follicles to grow in the ovaries. One of these follicles will develop to form a mature egg or ovum, which will be released in the middle of the menstrual cycle (day 14 of a 28-day menstrual cycle).

3. Ovulation

Ovulation generally occurs on about day 14 of the menstrual cycle. 

Ovulation refers to the release of a mature egg or ovum from the ovary, which is brought about by a sudden increase in LH hormone levels (LH surge).

4. Luteal (secretory) phase

The luteal phase begins after ovulation and ends just before the beginning of menstruation, occurring between days 15 to 28. 

During this phase, the egg released from the ovary travels to the uterus through the fallopian tubes. The hormone LH stimulates the secretion of progesterone, which causes the thickening of the uterine lining in preparation for pregnancy. If pregnancy does not occur, the progesterone levels fall, and the lining of the uterus is shed, marking the beginning of the menstrual phase.


Pelvic Pain: What's Causing Your Pelvic Pain? See Slideshow

At what ages does the menstrual cycle typically begin and end?

The beginning of menstruation, also called menarche, typically occurs between ages 11 and 14. Menarche may occur as early as 8 or as late as 16 years in some girls. 

Periods may continue until menopause, which is the cessation of the menstrual cycle. This generally occurs at about age 51. After menopause, ovulation does not occur, and you can no longer get pregnant naturally.

What are the symptoms of menstruation?

Bleeding from the vagina is a characteristic symptom of menstruation. Apart from bleeding, you may also experience the following:

When to see a doctor about your menstrual cycle

Menstruation is normal and typically does not require medical help. You may, however, need to see a doctor if you:

  • Do not start menstruating by the time you reach age 16
  • Have excessive bleeding (you have to change your tampon or pad after less than 2 hours or you pass clots the size of a quarter or larger)
  • Have bleeding that lasts more than 7 days
  • Suddenly stop getting periods
  • Notice bleeding or spotting between periods
  • Experience severe pain during periods
  • Think you may be pregnant
  • Experience disturbing mood changes during or around your periods
  • Have periods that do not start even after 3 months of stopping birth control pills and in the absence of pregnancy
  • Have a menstrual cycle shorter than 21 days or longer than 35 days
  • Experience a fever or feel sick after using tampons
  • Have suddenly irregular periods
  • Notice bleeding after sexual intercourse

What are the treatment options for menstrual pain?

Some pain during menstruation is normal; however, some women may experience severe cramps or mood changes before and during their periods. This is called premenstrual syndrome. You may also experience other bothersome symptoms such as vomiting, bloating, weight gain, and trouble concentrating. 

Most symptoms can be managed at home with the following measures:

If your menstrual cramps are severe, your doctor may recommend hormonal contraceptives to reduce the pain. Moreover, they may recommend vitamin supplements or transcutaneous electric nerve stimulation (a therapy that uses mild electric currents to stimulate your nerves) for pain relief. 

You can also try alternative strategies to manage pain and mood swings:

  • Aromatherapy
  • Acupressure
  • Acupuncture
  • Massage
  • Meditation

How can you track your menstrual cycle?

Tracking your menstrual cycle has several benefits, including determining your most fertile days and identifying any changes in your menstrual cycle that could be cause for concern. 

You can keep a track of your cycles by using a calendar or app. The calendar method, however, does not work if your cycles are shorter than 27 days. 

With the calendar method, the first day of your period is day 1. You should then keep marking the first day of your period for subsequent cycles. To know the duration of each cycle, count the number of days between the first days of each consecutive period. Do this for 6 cycles or more to accurately track your fertile days. 

To increase the accuracy of the calendar method, you can use it along with other fertility awareness methods such as cervical mucus and body temperature methods.

Table 1. Example of how can track your cycle
First day of period Number of days in a cycle
January 15 29
February 13 29
March 13 29
April 11 29
May 7 26
June 4 28
July 2 28
August 1 30

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How can you track your fertile days?

Your fertile days are when you are likely to get pregnant if you have unprotected sex. 

  • To calculate the first day of your fertile period: Subtract 18 from your shortest cycle (28 days in the above example), which gives you a number 10. Now count the number of days from the first day of your menstrual cycle (when your period begins). For example, if your period started on October 1, the first day of your fertile period would be October 10. 
  • To calculate the last day of your fertile period: Subtract 11 from your longest cycle. This is 30 days in the above example, which gives you 19. Count 19 from the first day of your period to know the last day of your fertile period. If you got your period on October 1, the last day of your fertile period is October 19. Thus, in this example, your fertile days are from October 10 to 19.

Some people use the calendar method as a means of birth control, avoiding sex during their “fertile days.” However, this is not as reliable or effective as the conventional means of birth control such as condoms and hormonal contraceptives. Furthermore, you need to track your periods for at least 6 months before you can use the calendar method to help with birth control. 

Table 2. Example of how to track your fertile days

Oct 1 (period starts) 

Oct 2                  Oct 3                  Oct 4                  Oct 5                  Oct 6                  Oct 7                 
Oct 8 Oct 9

Oct 10

Oct 11 Oct 12 Oct 13 Oct 14

Oct 15

Oct 16 Oct 17 Oct 18 Oct 19 Oct 20 Oct 21

Oct 22

Oct 23 Oct 24 Oct 25 Oct 26 Oct 27 Oct 28

Oct 29

Oct 30 Oct 31

Green = Not fertile

Red = Fertile

Medically Reviewed on 11/4/2022
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