Menarche is a female’s first menstrual period and a landmark event for females during puberty. Historically, menarche has been thought of as a time when women were “unclean.” However, cultural acceptance and scientific knowledge of menarche has greatly increased. Menarche occurs as part of the typical progression of puberty caused by rises in luteinizing hormone (LH), follicle stimulating hormone (FSH), and estrogen. The achievement of menstruation is associated with reproductive capability. Menarche that occurs earlier or later than expected should be evaluated by an experienced clinician and may signal a serious underlying problem. Currently, researchers are evaluating whether menarche is occurring earlier than in years past. An area of concern is whether environmental chemicals are affecting the timing of puberty.
Stockburger, Stephanie and Omar, Hatim A., "Menarche" (2014). Pediatrics Faculty Publications. 178.