The normal ovulatory menstrual cycle requires the presence of a mature hypothalamic-pituitary-ovarian axis and highly coordinated hormonal feedback loops. Consisting of three phases (follicular, ovulatory, and luteal), the normal menstrual cycle results in the formation of a mature follicle and release of an oocyte during each cycle, with menses occurring in the absence of fertilization. While adolescents may initially experience anovulatory cycles following menarche, the vast majority of cycles will be fairly regular, lasting 21 to 45 days in length with an average of three to seven days of bleeding. Absence of menarche by age 15, absence of menses for three consecutive months, and menses lasting eight days or longer with or without associated heavy bleeding are among the menstrual abnormalities that warrant further evaluation. Obtaining the menstrual history in adolescents with the knowledge of expected menstrual patterns allows the pediatric practitioner to provide appropriate counseling and education to adolescents and their families, and to identify menstrual abnormalities when they arise. Treating the menstrual cycle as a “vital sign” highlights the importance of normal menses as an indicator of an individual's overall health and enables timely identification of any concerning findings.

正常的排卵月经周期需要成熟的下丘脑-垂体-卵巢轴和高度协调的激素反馈回路。正常的月经周期由三个阶段（卵泡期、排卵期和黄体期）组成，每个周期都会形成一个成熟的卵泡并释放一个卵母细胞，而月经是在没有受精的情况下发生的。虽然青少年最初可能在初潮后经历无排卵周期，但绝大多数周期将相当规律，持续 21 至 45 天，平均出血 3 至 7 天。15 岁前没有初潮，连续三个月没有月经，月经持续 8 天或更长时间，伴有或不伴有大量出血，属于需要进一步评估的月经异常。在了解预期月经模式的情况下获取青少年的月经史，可以让儿科医生为青少年及其家人提供适当的咨询和教育，并在月经异常出现时识别它们。将月经周期视为“生命体征”强调了正常月经作为个人整体健康指标的重要性，并能够及时识别任何相关发现。