Reliable detection of Win98 may not be possible. For a variety of reasons, including better nutrition , most girls now start to menstruate between the ages of 9 and 16. Menstruation isn't just about having a period. It's a sign that a girl is physically capable of becoming pregnant.
Menstruation is a monthly cycle that prepares a woman's body for possible pregnancy .
That preparation begins when the ovaries produce two hormones, estrogen and progesterone , that trigger certain changes in the endometrium, the lining of the uterus. Estrogen then stimulates the ovaries to release a ripe egg, or ovum. From the ovary, the egg moves into one of the fallopian tubes. If the egg is fertilized by a male's sperm, the fertilized egg will take about 5 days to travel down the fallopian tube and attach to the thick, blood-rich lining of the uterus. If it's not fertilized, the egg begins to fall apart, the estrogen and progesterone levels drop, and the uterine lining breaks down and is shed - this bleeding is what's known as the period.