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6975029 
Book/Book Chapter 
Physiology, menarche 
Lacroix, AE; Gondal, H; Langaker, MD 
2020 
StatPearls Publishing 
Treasure Island, FL 
StatPearls 
English 
29261991 
Menarche is the occurrence of a first menstrual period in the female adolescent. Menstruation is the monthly shedding of the functional layer of the uterine endometrial lining that occurs when ovulation is not followed by fertilization. It occurs approximately every 28 days, with a range from every 21 to every 45 days. The average age of onset of menarche is 12.4 years. Most menstrual periods last between 3 and 7 days, and menses that last more than 10 days is considered abnormal. Menarche signals maturation of the adolescent female body. It commonly is associated with the ability to ovulate and reproduce. However, the appearance of menarche does not guarantee either ovulation or fertility.