Many young females experience degrees of menstrual irregularity during their adolescence, especially in the first two years after menarche, due to higher frequency of anovulatory cycles (
12,
19). The 5th and 95th percentiles for cycle length within the first gynecologic year are 18.3 and 83.1 days (
12). Previous studies on variation of the menstrual cycle length showed that maturation of the hypothalamic-pituitary-ovarian axis can take up to five years after menarche (
20,
21), whereas recent studies reported that regular menstrual patterns can be established within 6 to 12 months of menarche (
22-
24). Generally, there is a misconception that any degree of amenorrhea or menstrual irregularity during adolescence is normal and result of the natural process of puberty, whereas it should be considered that menstrual cycles of adolescent females differs only slightly from those of their aged counterparts (
1). Endocrine society clinical guidelines suggest that an abnormal menstrual bleeding due to anovulation, if persistent, is a matter for concern (
18). The precise definition of persistent oligo-anovulation in adolescents is yet imprecise for diagnosing PCOS (
12), with some investigators suggesting that this finding should be present for at least two years after menarche, or primary amenorrhea at the age of 16 years (
11). Since the risk of anovulation is greater in adolescents with HA than in their non-HA counterparts, females with anovulation manifestations should be evaluated for HA (
25). Indeed, menstrual cycles intervals < 20 or > 90 days are abnormal even in the first post-menarcheal year and require further investigation (
12).