Karen Sarpolis, MD

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Physical Signs That Precede First Menstruation

While girls vary in the ages that they are when they start their periods and when the other signs of puberty occur, the order is fairly consistent. The two things that are most closely tied to the age when a girl starts her periods, that she can readily assess herself are: first real bra and armpit hair. A "real" bra means one with a cup size attached to it, as opposed to small, medium, large distinctions. Armpit hair is self-explanatory. Any amount will do. At this point, a girl will probably start her periods within 3-6 months, if she hasn't already.

It also occurs right after the growth spurt of adolescence. So, if a girl grew, grew, grew, last year and has slowed down (no more than 2.5 inches a year) then periods are right around the corner.

Average Ages And Average Time Between Stages

Another way to estimate is to remember when it all started. The very first sign is called breast budding. Budding simply means the nipple elevates a bit. It does not mean the girl has development that resembles a breast. This is later. To remember when this is, a girl should think of when the very, very first time was that she noticed anything different about her chest. In some girls, pubic hair is first, or at least the first thing she remembers. Again, any amount will do. It will take an average of 4 1/2 years from this point, with a range of 1 1/2 to 6 years).

Take this as the starting point or adolescence. Here is the sequence and time frame of events for an average girl. The girl will also begin her growth spurt about this time. She will notice pubic hair about 6 months later. About 6 months after that (a total of one year after budding) she will be in her peak growth spurt, growing faster that she ever has. She will probably get her first training bra at this time. About a year after all this (a total of two years after budding), she will get a real bra and armpit hair. First period will come about 4 months before or after these events.

Your actual mileage may vary. So, the chart below gives the events and their ranges. The average age for periods in the U.S. is 12.16 for black girls and 12.88 for whites. By age 11, 28% of black girls and 13.5% of whites menstruate. By age 12, 62% of blacks, and 35% of whites.

A girl's first menstruation is called menarche. This is pronounced MEN-arc or MEN-arc-y. When a girl passes certain milestones in her development, but does not start having periods, this is called Primary Amenorrhea. This is pronounced A-men-or-rea or Ah-men-or-rea. The word primary is the part that means the girl has never had a period. The amenorrhea part means lack (a is Latin for none) of periods (menorrhea is Latin for "monthly flow"). This is to distinguish it from Secondary Amenorrhea, which is when a woman has had periods and then stops.

These standards were developed long ago. Meanwhile the average age of puberty and menarche has dropped. So, Estronaut's opinion is that checking with a doctor a year or so earlier is not a bad idea. Also, girls of African descent mature sooner than Europeans, by about a year. So, these girls should substract another year. (We have not been able to find averages for other races.)

On age alone: Age 15 1/2 to 16 1/2 for whites, age 14 1/2 to 15 1/2 for blacks.

If no breast or hair development: Age 13 to 14 for whites, age 12 to 13 for blacks.

If there is breast development or hair (pubic or armpit)two years after either of these started.

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When will girls get their first period? The ages vary, but there are two signs of puberty that generally precede first menstruation.

Author | Karen Sarpolis, MD

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First Menstruation: Average Age and Physical Signs