What are the stages and features of normal menstruation?

Onset of Menstruation (Menarche).

Previous evidence had set the onset of menstruation, called the menarche, at an average of age 12 or 13. 

Recent studies, however, set the time of onset earlier by about one year in Caucasian girls and two years in African American girls. 

Currently, the youngest possible age for normal puberty is 7 years old for Caucasians and 6 years old for African Americans, down from a previous low of 8 years for both. 

Evidence is pointing to the increasing incidence of childhood obesity as a major cause of the trend in earlier menarche onset. (Obesity is also highly associated with hormonal disorders in girls entering puberty at young ages.) Environmental estrogens found in chemicals and pesticides are also suspects. 

Typical Menstrual Cycle

Menstrual Phases

Typical No. of Days

Hormonal Actions

Follicular (Proliferative) Phase

Cycle Days 1 through 6: Beginning of menstruation to end of blood flow.

Estrogen and progesterone start out at their lowest levels. 

FSH levels rise to stimulate maturity of follicles. Ovaries start producing estrogen and levels rise, while progesterone remains low.


Cycle Days 7 – 13: The endometrium (the inner lining of the uterus) thickens to prepare for the egg implantation.



Ovulation Cycle Day 14:

Surge in LH. Largest follicle bursts and releases egg into fallopian tube.

Luteal (Secretory) Phase, also known as the Premenstrual Phase

Cycle Days 15 – 28: Ruptured follicle develops into corpus luteum, which produces progesterone. Progesterone and estrogen stimulate blanket of blood vessels to prepare for egg implantation.


If fertilization occurs:

Fertilized egg attaches to blanket of blood vessels that supplies nutrients for the developing placenta. Corpus luteum continues to produce estrogen and progesterone.


If fertilization does not occur:

Corpus luteum deteriorates. Estrogen and progesterone levels drop. The blood vessel lining sloughs off and menstruation begins.


Length of Monthly Cycle.

The menstrual cycle can be very irregular for the first one or two years, usually being longer than the average of 28 days. 

The length then generally stabilizes to an average of 28 days, although the cycle length may range from 20 to 45 days and still be considered normal. 

When a woman reaches her 40s the cycle lengthens, reaching an average of 31 days by age 49. 

A number of factors can affect cycle length at any age. 

Risk Factors for Shorter Cycles

Risk Factors for Longer Cycles

Regular alcohol use.

Being under 21 and over 44.

Stressful jobs.

Being very thin (also at risk for short bleeding periods).


Competitive athletics (also at risk for short bleeding periods)

Length of Periods.

Periods average 6.6 days in young girls. 

By the age of 21, menstrual bleeding averages six days until women approach menopause. 

However, that about 5% of healthy women menstruate less than four days and 5% menstruate more than eight days. 

Normal Absence of Menstruation.

Normal absence of periods can occur in any woman under the following circumstances: 

  • Menstruation stops during the duration of pregnancy. Some women continue to have irregular bleeding during the first trimester. This bleeding may indicate a threatened miscarriage and requires immediate attention by the physician. 
  • When women breastfeed they are unlikely to ovulate. After that time, menstruation usually resumes and they are fertile again. 
  • Perimenopause starts when the intervals between periods begin to lengthen, and it ends with menopause itself (the complete cessation of menstruation). 
  • Menopause usually occurs at about age 51, although smokers often go through menopause earlier.