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A female’s first menstrual period, known as menarche, occurs during puberty. Menstruation indicates that the body is mature enough for reproduction. About 98% of girls begin their periods by age 15.

There is unexpectedly large variation in height growth in girls after their first period. Every second girl grows either more or less in length than the 6–8 centimeters that is considered standard.

There is unexpectedly large variation in height growth in girls after their first period. Every second girl grows either more or less in length than the 6-8 centimeters that is considered standard.

SAN FRANCISCO—A grandfather’s exposure to endocrine-disrupting chemicals may impact the age when his granddaughter starts her first period, according to preliminary data being presented Sunday at ENDO ...