Menarche: The first MENSTRUAL CYCLE marked by the initiation of MENSTRUATION.Puberty, Delayed: The lack of development of SEXUAL MATURATION in boys and girls at a chronological age that is 2.5 standard deviations above the mean age at onset of PUBERTY in a population. Delayed puberty can be classified by defects in the hypothalamic LHRH pulse generator, the PITUITARY GLAND, or the GONADS. These patients will undergo spontaneous but delayed puberty whereas patients with SEXUAL INFANTILISM will not.Puberty: A period in the human life in which the development of the hypothalamic-pituitary-gonadal system takes place and reaches full maturity. The onset of synchronized endocrine events in puberty lead to the capacity for reproduction (FERTILITY), development of secondary SEX CHARACTERISTICS, and other changes seen in ADOLESCENT DEVELOPMENT.Puberty, Precocious: Development of SEXUAL MATURATION in boys and girls at a chronological age that is 2.5 standard deviations below the mean age at onset of PUBERTY in the population. This early maturation of the hypothalamic-pituitary-gonadal axis results in sexual precocity, elevated serum levels of GONADOTROPINS and GONADAL STEROID HORMONES such as ESTRADIOL and TESTOSTERONE.Reproductive History: An important aggregate factor in epidemiological studies of women's health. The concept usually includes the number and timing of pregnancies and their outcomes, the incidence of breast feeding, and may include age of menarche and menopause, regularity of menstruation, fertility, gynecological or obstetric problems, or contraceptive usage.Age Factors: Age as a constituent element or influence contributing to the production of a result. It may be applicable to the cause or the effect of a circumstance. It is used with human or animal concepts but should be differentiated from AGING, a physiological process, and TIME FACTORS which refers only to the passage of time.Menstruation Disturbances: Variations of menstruation which may be indicative of disease.Menopause: The last menstrual period. Permanent cessation of menses (MENSTRUATION) is usually defined after 6 to 12 months of AMENORRHEA in a woman over 45 years of age. In the United States, menopause generally occurs in women between 48 and 55 years of age.Parity: The number of offspring a female has borne. It is contrasted with GRAVIDITY, which refers to the number of pregnancies, regardless of outcome.Menstruation: The periodic shedding of the ENDOMETRIUM and associated menstrual bleeding in the MENSTRUAL CYCLE of humans and primates. Menstruation is due to the decline in circulating PROGESTERONE, and occurs at the late LUTEAL PHASE when LUTEOLYSIS of the CORPUS LUTEUM takes place.Body Height: The distance from the sole to the crown of the head with body standing on a flat surface and fully extended.Sexual Development: The processes of anatomical and physiological changes related to sexual or reproductive functions during the life span of a human or an animal, from FERTILIZATION to DEATH. These include SEX DETERMINATION PROCESSES; SEX DIFFERENTIATION; SEXUAL MATURATION; and changes during AGING.Menstrual Cycle: The period from onset of one menstrual bleeding (MENSTRUATION) to the next in an ovulating woman or female primate. The menstrual cycle is regulated by endocrine interactions of the HYPOTHALAMUS; the PITUITARY GLAND; the ovaries; and the genital tract. The menstrual cycle is divided by OVULATION into two phases. Based on the endocrine status of the OVARY, there is a FOLLICULAR PHASE and a LUTEAL PHASE. Based on the response in the ENDOMETRIUM, the menstrual cycle is divided into a proliferative and a secretory phase.Body Mass Index: An indicator of body density as determined by the relationship of BODY WEIGHT to BODY HEIGHT. BMI=weight (kg)/height squared (m2). BMI correlates with body fat (ADIPOSE TISSUE). Their relationship varies with age and gender. For adults, BMI falls into these categories: below 18.5 (underweight); 18.5-24.9 (normal); 25.0-29.9 (overweight); 30.0 and above (obese). (National Center for Health Statistics, Centers for Disease Control and Prevention)Age of Onset: The age, developmental stage, or period of life at which a disease or the initial symptoms or manifestations of a disease appear in an individual.Contraceptives, Oral: Compounds, usually hormonal, taken orally in order to block ovulation and prevent the occurrence of pregnancy. The hormones are generally estrogen or progesterone or both.Risk Factors: An aspect of personal behavior or lifestyle, environmental exposure, or inborn or inherited characteristic, which, on the basis of epidemiologic evidence, is known to be associated with a health-related condition considered important to prevent.Adolescent Development: The continuous sequential physiological and psychological changes during ADOLESCENCE, approximately between the age of 13 and 18.Sexual Maturation: Achievement of full sexual capacity in animals and in humans.Growth: Gradual increase in the number, the size, and the complexity of cells of an individual. Growth generally results in increase in ORGAN WEIGHT; BODY WEIGHT; and BODY HEIGHT.Gymnastics: Systematic physical exercise. This includes calisthenics, a system of light gymnastics for promoting strength and grace of carriage.Gravidity: The number of pregnancies, complete or incomplete, experienced by a female. It is different from PARITY, which is the number of offspring borne. (From Stedman, 26th ed)Dysmenorrhea: Painful menstruation.Breast Neoplasms: Tumors or cancer of the human BREAST.Pregnancy: The status during which female mammals carry their developing young (EMBRYOS or FETUSES) in utero before birth, beginning from FERTILIZATION to BIRTH.Birth Weight: The mass or quantity of heaviness of an individual at BIRTH. It is expressed by units of pounds or kilograms.Longitudinal Studies: Studies in which variables relating to an individual or group of individuals are assessed over a period of time.Hair Preparations: Hair grooming, cleansing and modifying products meant for topical application to hair, usually human. They include sprays, bleaches, dyes, conditioners, rinses, shampoos, nutrient lotions, etc.Amenorrhea: Absence of menstruation.Cohort Studies: Studies in which subsets of a defined population are identified. These groups may or may not be exposed to factors hypothesized to influence the probability of the occurrence of a particular disease or other outcome. Cohorts are defined populations which, as a whole, are followed in an attempt to determine distinguishing subgroup characteristics.