The menstrual cycle — Health, 14–17 years
How hormone changes prepare the reproductive system, why cycles vary, and how menstruation fits into the larger pattern.
A repeating body pattern
The menstrual cycle is a changing pattern directed by hormones. An egg may mature, the womb lining becomes ready for a possible pregnancy, and if pregnancy does not happen, that lining leaves the body as menstrual bleeding. The length and symptoms can differ widely between people and from month to month.
Why the cycle changes
The reproductive system needs coordination: one hormone signal should not start every step at once. Hormones rise and fall in a sequence, preparing an egg and the womb at different times. Stress, illness, intense training, weight changes and puberty can shift this timing, so a calendar is a guide, not a promise.
Following one cycle
Suppose bleeding starts on 3 March and the next bleeding starts on 31 March. Count the first day of bleeding as day 1: 3 March is day 1, and 31 March is the first day of the next cycle, so this cycle lasted 28 days. That number describes this cycle only; it cannot guarantee when the next one will begin.
The 28-day rule
A common mistake is to treat 28 days as the correct cycle length for everyone, or to count from the last day of bleeding. It is reasonable because 28 days is often used in examples and calendars. The useful count starts on the first day of bleeding, and real cycles can be shorter, longer or irregular.
Health tracking
Recording bleeding dates, pain, mood and other symptoms can reveal a personal pattern and make a healthcare conversation clearer. It can also help plan supplies or notice a change. Seek medical advice for very heavy bleeding, severe pain, fainting or a sudden persistent change; tracking is information, not a diagnosis.
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