The Menstrual Cycle

After reaching sexual maturity during puberty and completing their natural development, women experience vaginal bleeding on average every 28 days. Not every woman menstruates at the same interval or for the same duration. However, a cycle occurring every 21–35 days is considered natural. The duration of the period itself can also range from 2–7 days. What matters is that the bleeding starts light, builds to a peak, and then gradually tapers off until it ends.

Each month, several egg follicles in the ovaries begin to mature. During this time, the uterine lining also thickens and develops a richer blood supply.

The most developed of the maturing egg follicles ruptures its follicle and is released from the ovary.

The egg is then drawn in by the fine, finger-like projections at the ends of the fallopian tubes.

A woman's egg remains viable for 24 hours; if it encounters sperm within the tube during this time, fertilization occurs. The fertilized egg is then carried from the tube into the uterus and implants in the uterine wall.

If fertilization does not occur, the uterine tissue that had developed to receive the egg is shed along with bleeding.

This process — menstruation — occurs on average every 28 days in women, though this can range from 21 to 35 days from woman to woman. A few days' variation each month is normal. Even when this timing varies, ovulation always occurs approximately two weeks before menstruation.

The days just before and after ovulation are the most fertile window for conception, since sperm can remain viable in the female body for 5–7 days.

Menstrual bleeding is not the shedding of "dirty" blood, nor is it bleeding in the sense of an injury.

Likewise, since this bleeding does not result from any cut or injury, menstruation should never be perceived as an illness or disability.