The first menstrual bleeding is referred to as menarche, which typically occurs about two years after thelarche. Thelarche is a term used to refer the onset of secondary breast development. The experience of menarche, is different for different girls, it may happen when they are between the age group 11 to 16. The time period between the menstrual period also known as menses, is not always regular in the first two years. Ovulation may or may not be accompanied with the earliest menses, but it is necessary for fertility. Initiation of ovulation after menarche is inescapable. Those girls with irregularity in menstrual cycle for a long period of time are at a higher risk of prolonged irregularity and reduced fertility.