Puberty<unk>  is the culmination of a series of physiological and anatomic processes of puberty: * Attainment of a sufficient body mass (typically 17% body fat). * Disinhibition of the GnRH pulse generator in the arcuate nucleus of the hypothalamus. * Secretion of estrogen by the ovaries in response to pituitary hormones. * Over an interval of about 2 to 3 years, estrogen stimulates growth of the uterus (as well as height growth, breast growth, widening of the pelvis, and increased regional adipose tissue). * Estrogen stimulates growth and vascularity of the endometrium, the lining of the uterus. * Fluctuations of hormone levels can result in changes of adequacy of blood supply to parts of the endometrium. * Death of some of the endometrial tissue from these hormone or blood supply fluctuations leads to deciduation, a sloughing of part of the lining with some blood flow from the vagina. No specific hormonal signal for<unk>  is known;<unk>  as a discrete event is thought to be the relatively chance result of the gradual thickening of the endometrium induced by rising but fluctuating pubertal estrogen. The menstruum, or flow, consists of a combination of fresh and clotted blood with endometrial tissue. The initial flow of<unk>  is usually brighter than mature menstrual flow. It is often scanty in amount and may be very brief, even a single instance of "spotting". Like other menses,<unk>  may be accompanied by abdominal cramping. Relation to fertility In most girls,<unk>  does not mean that ovulation has occurred. In postmenarchal girls, about 80% of the cycles were anovulatory in the first year after<unk> , 50% in the third and 10% in the sixth year. Regular ovulation is usually indicated by predictable and consistent intervals between menses, predictable and consistent durations of menses, and predictable and consistent patterns of flow (e.g., heaviness or cramping). Continuing ovulation typically requires a body fat content of at least 22%. An anthropological term for this state of potential fertility is nubility. On the other hand, not every girl follows the typical pattern, and some girls ovulate before the first menstruation. Although unlikely, it is possible for a girl who has engaged in sexual intercourse shortly before her<unk>  to conceive and become pregnant, which would delay her<unk>  until after the end of the pregnancy. This goes against the widely held assumption that a woman cannot become pregnant until after<unk> . A young age at<unk>  is not correlated with a young age at first sexual intercourse. Onset When<unk>  occurs, it confirms that the girl has had a gradual estrogen-induced growth of the uterus, especially the endometrium, and that the "outflow tract" from the uterus, through the cervix to the vagina, is open. When a woman experiences<unk> , the blood flow can vary from a slow and spotty discharge to a consistent blood flow for 3-7 days. While the color of the blood does range from a brown to bright red color, this is normal; some women have light periods while others have heavy ones; everyone is different. In very rare instances,<unk>  may occur at an unusually early age, preceding thelarche and other signs of puberty. This is termed isolated premature<unk> , but other causes of vaginal bleeding must be investigated and excluded. Growth is usually normal. Isolated premature<unk>  is rarely the first manifestation of precocious puberty. When<unk>  has failed to occur for more than three years after thelarche, or beyond 16 years of age, the delay is referred to as primary amenorrhea. Timing Chronic illness Certain systemic or chronic illness can delay<unk> , such as undiagnosed and untreated celiac disease (which often occurs without gastrointestinal symptoms), asthma, diabetes mellitus type 1, cystic fibrosis and inflammatory diseases, among others. In some cases, because biochemical tests are not always discriminatory, underlying pathologies are not identified and the girl is classified as constitutional growth delay. Short stature, delayed growth in height and weight, and/or delayed<unk>  may be the only clinical manifestations of celiac disease, in absence of any other symptoms. According to a review article, there may also be an association between early age at<unk>  and breast cancer risk. Conditions and disease states Studies have been conducted to observe the association of the timing of<unk>  with various conditions and diseases. Some studies have shown that there may be an association between early or late-age<unk>  and cardiovascular disease, although the mechanism of the association is not well understood. A systematic review has concluded that early age at<unk>  is also a risk factor for the insulin resistance condition. There is conflicting evidence regarding the association between obesity and timing of<unk> ; a meta-analysis and systematic review has determined that more studies must be conducted to make any definitive conclusions about this association. Effects of stress and social environment Some of the aspects of family structure and function reported to be independently associated with earlier<unk>  antenatal and early childhood * Being non-white * Having experienced pre-eclampsia in the womb * Being a singleton, i.e. not a twin, triplet, etc. * Low birthweight * Not having been breast-fed * Previous exposure to smoking * High-conflict family relationships * Increased incidence of childhood obesity. * Lack of exercise in childhood Other research has focused on the effect of childhood stress on timing of puberty, especially female. Stress is a vague term and studies have examined conditions ranging from family tensions or conflict to wartime refugee status with threat to physical survival. The more dire social conditions have been found to be associated with delay of maturation, an effect that may be compounded by dietary inadequacy. There is more uncertainty and mixed evidence as to whether milder degrees of stress or early-life under-nutrition can accelerate puberty in girls as would be predicted by life history theory and demonstrated in many other mammals. The understanding of these environmental effects is incomplete and the following observations and cautions are relevant: * Mechanisms of these social effects are unknown, though a variety of physiological processes, including pheromones, have been suggested based on animal research. * Most of these "effects" are statistical associations revealed by epidemiologic surveys. Statistical associations are not necessarily causal, and a variety of secondary variables and alternative explanations can be possibly intervening. Effects of such small size can never be confirmed or refuted for any individual child. * Despite the small magnitude of effect, interpretations of the data are politically controversial because of the ease with which this type of research can be used for political advocacy. Accusations of bias based on political agenda sometimes accompany scientific criticism. * Correlation does not imply causation. While correlation can be objectively measured, causation is statistically inferred. Some suggest that childhood stress is caused by precocious puberty recognized later, rather than being the cause of it. Changes in time of average age Secular trend in decrease in age of<unk>  in Western European and North American girlsAfter: Boaz (1999) There were few systematic studies of timing of<unk>  before the later half of the 20th century. Most older estimates of average timing of<unk>  were based on observation of a small homogeneous population not necessarily representative of the larger population, or based on recall by adult women, which is also susceptible to various forms of error. Most sources agree that the average age of<unk>  in girls in modern societies has declined, though the reasons and the degree remain subjects of controversy. From the sixth to the fifteenth centuries in Europe, most women reached<unk>  on average at about 14, between the ages of 12 and 15. A large North American survey reported only a 2–3 month decline from the mid-1970s to the mid-1990s. A 2011 study found that each 1 kg/m2 increase in childhood body-mass index (BMI) can be expected to result in a 6.5% higher absolute risk of early<unk>  (before age 12 years). Fewer than 10% of U.S. girls start to menstruate before 11 years of age, and 90% of all U.S. girls are menstruating by 13.8 years of age, with a median age of 12.4 years. This age at<unk>  is not much different (0.3 years earlier) than that reported for U.S. girls in 1973. Age at<unk>  for non-Hispanic black girls was significantly earlier than that of white girls at 10%, 25%, and 50% of those who had attained<unk> , whereas non-white Mexican American girls were only slightly earlier than the white girls at 25%.
Menarche
Thelarche
Spermarche
Gonadarche
Pubarche
Sunovion
Adrenarche
Menstruation