the first menstrual bleeding (period). The usual age range is from 10-15 with the average about 12.5 years. The age of menarche has dropped (called the "secular trend") during the past century but the age of menarche now appears to be stabilizing in developed countries in the 21st century.
Menarche (IPA: ) is the first menstrual period, or first menstrual bleeding. From both social and medical perspectives it is often considered the central event of female puberty, as it signals the possibility of fertility. Timing of menarche is influenced by both genetic and environmental factors, especially nutritional status.