The menstrual cycle

The idea

The onset of the menstrual cycle is an important internal change in adolescent girls; the cycle generally recurs every 28–30 days, though healthy cycles may range from 21 to 35 days.

A cycle that repeats

In adolescence a girl's body begins a natural process called the menstrual cycle, which is more commonly known as the period. It does not happen just once. It comes round again and again.

How often do you think the cycle generally comes round?

• Every few days
• About every four weeks
• Only once a year

Cycles on a calendar

Press + and − to change the length of one cycle. Watch how the cycles repeat along the days. Find the shortest, the usual and the longest cycle.

The menstrual cycle

The onset of the menstrual cycle is an important internal change in adolescent girls. It recurs generally every 28 to 30 days. Many healthy girls have longer or shorter cycles, ranging from 21 to 35 days.

The menstrual cycle is an important natural process and one of the signs of good reproductive health.

• Cycle length | What it means
• 28 to 30 days | generally, how often the cycle recurs
• 21 to 35 days | the range of many healthy girls, with longer or shorter cycles

Notes

The onset of the menstrual cycle is an important internal change in adolescent girls. It recurs generally every 28 to 30 days, and healthy cycles may range from 21 to 35 days.

Check yourself

Generally, how often does the menstrual cycle recur?

Anita's cycle is 24 days long. Priya's cycle is 33 days long. What can we say?

A girl's cycle recurs every 28 days. How many complete cycles does she have in 84 days?

Answer: 3

Three: 84 days ÷ 28 days = 3 cycles. The cycle keeps recurring.

What kind of change is the onset of the menstrual cycle in adolescent girls?

• Every 28 to 30 days — correct. Yes! That is how often it generally comes round.
• Every few days. It comes round much less often than that.
• Only once in a year. It recurs far more often than once a year.
• Only Anita's cycle is in the healthy range. Priya's 33 days is also inside the range of 21 to 35 days.
• Both are inside the range of 21 to 35 days — correct. Yes! Many healthy girls have longer or shorter cycles like these.
• Only Priya's cycle is in the healthy range. Anita's 24 days is also inside the range of 21 to 35 days.
• An external change that everyone can easily see. It happens inside the body, so it is an internal change.
• A sign that something is wrong with the body. It is a natural process and a sign of good reproductive health.
• An internal change; it is a natural process — correct. Yes! It is an important internal change.