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The Informed Parent

Menarche—When Should Menses Start?

by Louis P. Theriot, M.D., F.A.A.P.
Published on Sep. 23, 2013

Lara, a 13-year-old girl, came to the office for her yearly physical accompanied by her mother. An excellent student and completive volleyball player, she was very engaging as I asked my questions. She did most of the talking until I asked if she had started having her periods. Clearly this was a sensitive area. That is when mom started to do the talking.

Lara folded her arms and seemed to be a bit uncomfortable. Mom said, “I’m glad you brought this up. I’ve been very concerned and Lara doesn’t want to talk about it. My periods started before my 13th birthday, and Lara hasn’t started yet. I’m thinking I should take her to an endocrine specialist or a gynecologist. What do you think?”

First I needed to finish taking the history, followed by the routine examination. THEN I could answer their questions. Lara was in excellent shape and had a perfectly normal exam. She had significant breast development, pubic and axillary hair. This became evident within the past eight months. Everything looked normal and I would expect her periods to start within the next few months.

Most women will start their periods within a year of when their mother’s started…plus or minus a year. Since she had the secondary sexual characteristics of breast development, pubic and axillary hair, the hormonal component of puberty seemed adequately in place. When this occurs, the periods usually will start within a year. I then went on to give them some statistics about puberty.

The median age for menarche, the onset of periods or menstruation, in the United States is 12.4 years. Most girls will start having their periods by the age of 14 years (over 95%). Once the periods start, it is very common for the periods to be very sporadic or irregular for the first 1-2 years after which they should be more regular. A normal menstrual cycle in an adult is every 21-35 days, and lasts 3-7 days.

The secondary sexual characteristics of breast development (thelarche) and pubic hair (pubarche) precede the onset of menses. The average age of onset of thelarche in the United States is 10.2 years. For pubarche, the average age of onset is 11.6 years. If a girl shows no signs of secondary sexual characteristics by 13 years of age, this is considered abnormal and MUST be evaluated.

If the secondary sexual characteristics start too early, this can be abnormal and is called precocious puberty. It used to be accepted that any breast development or pubic hair before the age of 8 was considered precocious puberty. But recent reports show that certain young women are starting to develop much earlier than in previous generations. These include obese girls, girls of African-American descent and girls of Mexican-American descent. One paper showed that 27% of African-American girls showed signs of puberty at 7 years of age compared to 7% of white girls. While this has been shown in numerous studies, it seems that the age of menarche has remained fairly constant. 

It is considered abnormal if girls have not had any secondary sexual characteristics by the age of 13 years. It is also abnormal if they have not had their periods by 15 years of age (considered primary amenorrhea), or have not started having their periods within 3 years of breast development and the presence of pubic hair. In these situations a girl must be medically evaluated and should see an endocrinologist.

Secondary amenorrhea occurs when a girl has not had a period for three months after the onset of menses. This warrants an evaluation and of course there should be concern for a pregnancy. However, there may be many other causes of this. These include eating disorders, stress, dramatic weight changes and drug use. A girl with secondary amenorrhea must be evaluated and this should not be taken lightly.

After our visit I could tell that Lara felt much more comfortable about things. This had bothered her more than she let on since most of her friends had been having their periods for a while. But the one who I feel was most relieved was mom.

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