What Menstrual Cycle Is Normal?

Often a question I get is “what is a normal menstrual cycle in a girl starting out and when should I worry?”

In girls, menstrual periods typically occur within 2–3 years after breast development. By age 15 years, 98% of females will have had their menstrual periods. An evaluation for primary amenorrhea or lack of menstrual periods, should be considered for any adolescent who has not had their period by age 15 years or has not had a menstrual period within 3 years of thelarche. Lack of breast development by age 13 years also should be evaluated. 

Menstrual cycles are often irregular during the teen years, especially in the time from the first cycle to the second cycle. Most girls bleed for 2–7 days during their menstrual cycles.  Often cycles will be within the range of 21–45 days although short cycles of less than 20 days and long cycles of more than 45 days can occur. By the third year after periods start, most menstrual cycles are 21–34 days long, similar to what we see in adults. 

Although a long interval between menstrual cycles is common in the teen years, it is uncommon for girls and adolescents to continue to not have periods for more than 3 months or 90 days.  Teens who go for more than 3 months between periods need to be seen and evaluated.

With regards to menstrual flow, if a girl is requiring changing of menstrual products every 1–2 hours, this is considered excessive, especially if she is having flow that lasts more than 7 days at a time.

It is important to educate girls and their families about their puberty and development and of what their menstrual period means. Girls will likely begin to menstruate approximately 2–3 years after breast development begins. Adolescent girls should understand that menstruation is a normal part of development. Girls should be taught on the use of feminine products and on what is considered normal menstrual flow.

It is very important for families to understand the normal menstrual patterns of adolescent girls, the ability to differentiate between normal and abnormal menstruation, and the skill to know how to evaluate the adolescent girl patient. Menstrual abnormalities that suggest the need for further evaluation are listed.

It is important that a girl be seen if she has:

Menstrual periods that:

• have not started within 3 years of breast development

• have not started by 14 years of age with signs of increased hair on their face

• have not started by 15 years of age

• occur more frequently than every 21 days or less frequently than every 45 days

• occur 90 days apart even for one cycle

• last more than 7 days

• require frequent pad or tampon changes (soaking more than one every 1–2 hours)

• are heavy and are associated with a history of excessive bruising or bleeding or a family history of a bleeding disorder

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If you have further questions about irregular menstrual cycles in your teens,

please contact me at drmehra@themehraclinic.com .