Expansion
Breast then pubic hair then growth spurt then menarche in girls; testicular enlargement first in boys
Expansion
Girls (typically 8 to 13 years at onset)
- Thelarche: breast budding, the first sign
- Pubarche: pubic hair
- Growth spurt, peaking at about Tanner stage 3
- Menarche, typically 2 to 2.5 years after thelarche, after peak height velocity
Boys (typically 9 to 14 years at onset)
- Testicular enlargement to over 4 ml, the first sign
- Pubic hair and penile growth
- Growth spurt, later, at about Tanner stage 4
- Voice change, facial hair, peak muscle mass
The timing difference explains adult height: boys have two extra years of prepubertal growth and a later, larger spurt.
The trigger is reactivation of pulsatile GnRH secretion, which has been quiescent since infancy. Leptin signals adequate energy stores, which is why very low body fat delays puberty and obesity may advance it.
Precocious puberty is defined as onset before 8 in girls and 9 in boys; delayed puberty as no signs by 13 in girls and 14 in boys.