In childhood, girls have relatively little GnRH, LH, FSH, oestrogen and progesterone in their system. During puberty, these hormones start to increase sequentially, causing the development of female secondary sexual characteristics, the onset of the menstrual cycle and the ability to conceive children.
Puberty starts age 8 – 14 in girls and 9 – 15 in boys. It takes about 4 years from start to finish. Girls have their pubertal growth spurt earlier in puberty than boys. Overweight children tend to enter puberty at an earlier age. Aromatase is an enzyme found in adipose (fat) tissue, that is important in the creation of oestrogen. Therefore, the more adipose tissue present, the higher the quantity of the enzyme responsible for oestrogen creation. There may be delayed puberty in girls with low birth weight, chronic disease or eating disorders, or athletes.
In girls, puberty starts with the development of breast buds, followed by pubic hair and finally the onset of menstrual periods. The first episode of menstruation is called menarche. Menstrual periods usually begin about two years from the start of puberty.
Tanner Staging
The stage of pubertal development can be determined using the Tanner scale, based on examination findings of secondary sexual characteristics.
|
Tanner Stage |
Approximate Age |
Pubic Hair |
Breast Development |
|
Stage I |
Under 10 |
No pubic hair |
No Breast Development |
|
Stage II |
10 – 11 |
Light and thin |
Breast buds form behind the areola |
|
Stage III |
11 – 13 |
Course and curly |
Breast begins to elevate beyond the areola |
|
Stage IV |
13 – 14 |
Adult like but not reaching the thigh |
Areolar mound forms and projects from surrounding breast |
|
Stage V |
Above 14 |
Hair extending to the medial thigh |
Areolar mounds reduce, and adult breasts form |
Hormonal Changes During Puberty
Growth hormone (GH) increases initially, causing a spurt in growth during the initial phases of puberty.
The hypothalamus starts to secrete GnRH, initially during sleep, then throughout the day in the later stages of puberty. GnRH stimulates the release of FSH and LH from the pituitary gland. FSH and LH stimulate the ovaries to produce oestrogen and progesterone. FSH levels plateau about a year before menarche. LH levels continue to rise, and spike just before they induce menarche.
Last updated April 2020