Menstrual Terminology 

The menarche is 1 of the later stages of puberty in girls. The average age of menarche in humans is 12 years, but is normal anywhere between ages 8 & 16. Factors such as heredity, diet & overall health could accelerate or delay menarche. The cessation of menstrual cycles at the end of a woman's reproductive period is termed menopause. The average age of menopause in women is 52 years in industrialised countries such as the UK, with anywhere between 45 & 55 being common. Menopause before age 45 is considered premature in industrialised countries. The age of menopause is largely a result of genetics however, illnesses, certain surgeries, or medical treatments might cause menopause to occur earlier.

The length of a woman's menstrual cycle will typically vary, with some shorter cycles & some longer cycles. A woman who experiences variations of less than 8 days between her longest cycles & shortest cycles is considered to have regular menstrual cycles. It is unusual for a woman to experience cycle length variations of less than 4 days. Length variation between 8 & 20 days is considered as moderately irregular cycles. Variation of 21 days or more between a woman's shortest & longest cycle lengths is considered very irregular .