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True precocious puberty differs from premature adrenarche and premature thelarche. Understanding normal sexual development and these common variants will help ob/gyns make the correct diagnosis and appropriate referrals.
Several reports have suggested, in the last decade or so, that normal girls are now maturing earlier than in the past. That research has prompted alarming write-ups in the popular press and brought many worried parents into the doctor's office. To help bring a balanced perspective to this issue, it's necessary to first review normal female puberty and emphasize the important difference between early breast development and early growth of pubic hair.
Of course, arriving at a balanced view also requires a closer look at the studies that suggest that, at least in the United States, puberty is starting earlier than in the past, and earlier in black girls than in white girls. We'll also discuss the phenomenon of isolated menses in prepubertal girls, and finally touch on what factors to weigh when deciding which girls need treatment. Our basic goal here is to help you decide when early puberty is likely to be a normal variant and can be observed, and when it should be promptly referred to a specialist for further evaluation.
Normal female puberty and normal variants
The first observable result is breast budding (thelarche) and enlargement of the nipples and areola; the growth spurt starts very soon thereafter. When examining chubby girls, you may find it challenging to make this distinction, but palpation should help you distinguish the firmer glandular breast tissue from the surrounding adipose tissue. The average time from breast budding to menarche, which requires the development of mid-cycle surges of LH, is about 2.5 years, but it varies widely from child to child.
Many clinicians don't realize how pubic and axillary hair fit into the process of pubertal maturation. Their appearance is unrelated to activation of the HPG axis but results from a developmental increase in adrenal androgen production, a process known as adrenarche, which often occurs at about the same time as gonadarche. A characteristic axillary odor generally appears around the same time. Although adrenarche frequently occurs around the same time as thelarche, in some normal girls pubic hair may appear several years before thelarche. When this occurs before age 8 as an isolated finding, it is called premature adrenarche. Parents can be reassured that this is a common normal variation with no implications for the age at menarche or the age at which growth is completed.
A second common normal variation is premature thelarche, in which breast tissue appears in a young girl, usually before 3 years of age, with either very slow or no progression over time, and normal growth. It is quite rare to see true precocious puberty before age 3 or ovarian tumors at any age, so the diagnosis can generally be made clinically. My review of 104 consecutive children (90 girls) evaluated for signs of early puberty found that premature adrenarche and premature thelarche together made up about two thirds of the girls referred.1
Is female puberty starting earlier?
The textbook definition of precocious female puberty is the appearance of breast tissue or pubic hair before age 8. Unfortunately that definition is based on a small number of US studies in the mid-1900s and a much better study of English white girls published in 1969, which placed the mean age of breast development at about 11, with very few girls reaching puberty before 8 years of age.2