Testosterone is an excellent parameter along with testicular size for the determination of the onset of puberty. A very marked increase in plasma bioactive LH in males was observed with age throughout puberty. In stage II, i.e. in early puberty, the first sign of onset of puberty in girls is the appearance of breast budding. Breast development is the most sensitive biological assay for assessing the secretion of estradiol, with or without the presence of pubic or axillary hair. Further stages are defined by the ongoing development of the breast, pubic and axillary hair, and the changes to the vulva and vagina.
Menarche represents stage V of pubertal development.
Menstrual cycles following menarche are not all necessarily ovulatory. The first ovulatory cycle usually occurs 10 months after menarche. None of them experienced breast budding before the age of 9 years, and all had some breast development at the age of 14. Early menarche was already observed in some girls at 11 years of age. All girls were menstruating by the age of 15 years.