Menstruation is monthly uterine bleeding out flowing through the vagina during reproductive life of a woman i.e. from menarche to menopause. It contains blood, cervical mucus, endometrial fragments & vaginal epithelium.

• Women have two ovaries, the organs that hold the ova, or eggs. There are thousands of eggs in each ovary. One egg is about as big as the tip of a pin.
• One of the first things to happen in the menstrual cycle is that an egg pops out of one of the ovaries. The egg travels from the ovary through the fallopian tube to the uterus, or womb. It is in the uterus where an egg grows into a baby.
• About the time the egg is traveling to the uterus, the uterus is building up a lining of healthy tissue and blood. If the egg reaches the uterus and is fertilized, it will remain there and become a baby. The lining is there to help the baby stay healthy and comfortable.
• But most of the time, the egg only “Visits” the uterus, then passes through. If the egg doesn’t remain in the uterus, the lining of blood and tissue is not needed and so it passes out through the vagina. It may seem like a lot of blood, but it's not. There is less than a half cup over the course of an entire period.
• About two weeks later, another egg works its way out and the entire cycle begins again. The whole menstrual cycle usually takes about one month from one period to the next.

Irregular Periods
Periods can be irregular at extremes of the reproductive life i.e. after menarche & nearing menopause. Otherwise periods should be regular.

Dysmenorrhoea
Dysmenorrhoea means painful menstruation. It is usually seen as stomach ache & backache. This is a normal phenomenon, which is a result of progesteron secretion. Occasionally there may be associated disorders like endometriosis, pelvic inflammation, fibroids etc.

Heaviness & tenderness in the breasts during menstruation
Some women do have heaviness & tenderness in the breasts during menstruation while some may have it premenstrually. If it is mild, only reassurance is the treatment.

Sex during menstruation
It is safe to have sex during menstruation since there are no chances of conception, however it is not hygienic.

Physical Activities during menstruation
It is advisable to restrict vigorous physical activities during menstruation but routine activities should be continued.