At the beginning of puberty, LH pulsatility is only present during sleep. It then extends to the daytime, with amplification of pulse amplitude and acceleration of frequency. This is accompanied by an increase in androgen plasma levels and ovarian enlargement, with acquisition of a multifollicular pattern.

These changes parallel those in the GH/IGF1 axis, whose hyperactivity induces a selective insulin resistance. This phenomenon results in a physiological hyperinsulinism which is responsible for the increase in insulin plasma level and decrease in SHBG and IGFBP-1 liver production.

The first menstrual cycles in adolescent girls are frequently anovulatory.
When compared to ovulatory cycles, they are characterized by higher serum levels of testosterone (T), androstenedione (A) and LH, with the possibility of mild hyperandrogenic symptoms. In most of adolescent girls, these abnormalities will spontaneously resume within 1 - 2 years, along with the regularization of their menstrual cycles. Conversely, in some others, they will worsen, with progressive constitution of PCOS features, such as hirsutism, anovulation, increased plasma T, A and LH levels and ovarian enlargement. At this time, however, it is difficult to distinguish biologically and ultrasonically those adolescents with such an evolution from the ones with ‘physiological mini-PCOS’due to the normal maturational process of puberty. Some features, however, are predictive (see below), in particular the association with oligomenorrhea which should not be viewed too quickly as a normal feature of the first gynecological years.