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The average age of menarche dropped from 14-15 years in the nineteenth century to 12-13 years in the present, but it seems that girls in the nineteenth century had a later age at menarche compared to girls in earlier centuries. [35] A large North American survey reported only a 2–3 month decline from the mid-1970s to the mid-1990s. [36]
The average age of a girl's first period is 12 to 13 (12.5 years in the United States, [6] 12.72 in Canada, [7] 12.9 in the UK [8]) but, in postmenarchal girls, about 80% of the cycles are anovulatory in the first year after menarche, which declines to 50% in the third year, and to 10% by the sixth. [9]
The average age of menarche is 12 to 15 years. [1] [8] However, it may occur as early as eight. [2] The average age of the first period is generally later in the developing world, and earlier in the developed world. [3] [9] The average age of menarche has changed little in the United States since the 1950s. [3]
Girls have started getting their first period earlier than in the past, so now it's considered "normal" for girls to get their period between 9 and 14 years old, says Maureen Whelihan, M.D., an ob ...
The average age at which puberty begins may be affected by ethnicity as well. For example, the average age of menarche in various populations surveyed has ranged from 12 [58] [59] [60] to 18 years. The earliest average onset of puberty is for African-American females and the latest average onset for high altitude subsistence populations in Asia.
“Among individuals born between 1950 and 2005, we found that younger generations were starting their first period (menarche) earlier, and the time it took for their periods to become regular ...
Called menarche, the first period occurs at the age of around twelve or thirteen years. [8] The average age is generally later in the developing world and earlier in the developed world. [42] In precocious puberty, it can occur as early as age eight years, [43] and this can still be normal. [44] [45]
The age of thelarche has been decreasing in the past few decades. Between 1973 and 2013, the age of thelarche decreased at a rate of 0.24 years per decade. [9] Other contemporary trends that may be contributing to this change in the onset of thelarche include increasing BMI, changes in pubertal timing, and environmental exposures.